An oft-repeated argument to defend Martin Brodeur is that it cannot be claimed that the trap is the reason for his success, since if it was, everyone else would just copy it. Other teams have not been able to emulate the Devils success, so it must be someone they have on their team that is the difference-maker. The main guy that has been there the whole time has been Martin Brodeur, so he should get the credit for the Devils' run of success.
This argument is partly correct, but is nevertheless wrong with respect to Martin Brodeur. It is true that if the strategic option of playing the trap dominated all others and did not depend on a team's talent level, then every team would use it and it would even itself out. But what matters is not the strategy alone, but how well that strategy is implemented. That is, how good is the team at playing the trap? Every team in the league plays a very defensive style with a one goal lead late in the third period, because it makes strategic sense, but clearly some teams are better than others at actually pulling it off.
A similar example I can use is the power play. Every team in the league has a power play unit, but some are better than others. Some teams are very good for a number of years on the power play (a recent example is the Detroit Red Wings, top 5 in the league in power play efficiency every year from 2000-01 to 2005-06). By similar logic to that above, it could be argued that other teams should be able to copy what they do and eliminate their advantage, but what is really driving the success is not just power play tactics, but also coaching, teamwork and talent. It wouldn't matter if the Chicago Blackhawks used the exact same power play setup as the Wings, moved the puck around in a similar manner and took the same types of shots, they just wouldn't be as effective.
It is glaringly obvious both on the statsheet and in real life that no matter how many teams used the trap, nobody played it as well as New Jersey. From 2000 to 2004, the worst New Jersey finished in fewest shots against was 2nd, and the most shots they allowed per game was 24.7. This was despite the other teams in the league having a decade to copy New Jersey's style. And it wasn't just Brodeur, since his average was actually 1.5 shots per game higher than his backups (who faced just 22.3 shots per game). Alan Ryder points out that the New Jersey Devils have always led the league in his measurements of shot quality against. This is a team where the immortal Corey Schwab had a 1.27 GAA in 14 games over 2 seasons. The Dead Puck Era New Jersey Devils were absurdly good at defence.
The Devils have generally had a deep defensive unit with a number of excellent defensive defencemen, as well as excellent defensive forwards on their checking line. This is still the case in New Jersey; it is easy to label newcomers like Johnny Oduya as untalented, but Oduya was on the ice for just 37 goals against in 1110 minutes of even-strength ice time this season, a good rate that was better than the rest of the team's when he wasn't playing (source: Behind the Net). Defensive play is hard to judge, but New Jersey seems to keep finding players who are very responsible in their own end, or perhaps developing them through their strong coaching staffs at the NHL or minor league level. The Devils are also very well managed by Lou Lamoriello, who usually brings in players that fit well into the New Jersey system. These are all reasons why New Jersey has been dominant defensively for over a decade, not merely the style of play that they employ.
There are, in fact, some teams that have copied the New Jersey model with some success. The best example is probably the Minnesota Wild, with Jacques Lemaire, although there are a number of other teams playing a tight defensive style, especially in the Western Conference. After the early years after expansion, Minnesota has been quite similar to New Jersey in team defensive statistics. Over the last few seasons, their goaltending has been every bit as good as New Jersey's in terms of save percentage. The Minnesota Wild have basically been the New Jersey Devils in a tougher division and with less overall talent. It is mainly those two factors that explain why the Devils have been at the top of their conference and the Wild have been in a constant struggle just to make the playoff struggle, not merely the choice of defensive style.
No strategy on its own will be successful if executed poorly, and, similarly, there are a number of strategies that will be successful if they are well-executed on a talented team. The Devils have won with a very defensive system mainly because they have done the best job of recruiting and developing talent that complements the system. Regardless of how many copycats there have been, it has only been since the lockout that a number of other teams have begun to rival New Jersey in terms of team defensive play. This coincides with significant talent losses for New Jersey (led of course by Stevens and Niedermayer). Without talent, no system of play is likely to be successful, and it has been primarily team defensive talent that has driven New Jersey's success. Even though some teams have copied New Jersey's tactics, nobody has played it as well as they have, and that is why Brodeur has had a relatively easy job throughout his entire career.