Please note that these number of deaths are compared to deaths in Afghanistan and not Iraq. We are talking a very limited number here and in reality, not many more than were getting injured or killed before. The real problem is that these guys are coming back from theater with loads of cash in the bank and are buying bikes and trying to ride without training.
Bikes are becoming an increasing problem with deaths and injuries in all sectors of life, not just military. As they become more and more popular, it is inevitable that more get killed or injured.
I can tell you that that quoted number of 350 since 2001 is a high, unrealistic number.