It's a good thing to let designers run free for 2 weeks I think - see what ideas formulate, see what ideas have been brewing for a while and finally have their chance. When working on 1 game for a long time, it gets very tedious, to the point where a lot of people just can't keep pushing and finish their game. I guess this is a bit like one of those development jam competitions, where people take on a 2 week project, or even a 1 week, or 1 weekend project... but done internally.
Really I don't think everyone realises just how tough it can be to develop the same game for years, a 2-week break might just be enough to save the project from mediocrity, let the designers and artists get their ideas off their chest, then get back to the job in hand. It's about as close to a summer vacation as most programmers get
.