And when does that ever happen? The prospects and assets the Devils dropped were chump change compared to what most teams do for a few rentals. Just last year, the Bruins traded a former 1st, a 1st, and 2nd to get Kaberle.
The Devils, luckily, gave up almost nothing to get a player who had a bigger impact than Kaberle. Even when a team has constructed a roster where you don't have to do this, the GM feels the pressure to do something anyway and usually overpays for some crap.
There have been years where the Devils have barely made any deadline deals. In 2009, the Devils traded a guy they signed as an undrafted free agent to get a defenseman. This year the Devils spent a 2nd, 3rd, 4th, and 7th round pick to improve the roster, plus a guy who'd still be mildly useful to have around in Nick Palmieri. Still, you'd prefer to not have to do that.