The fact is most of the yeshiva boys ARE doing a service for the nation; it's just not called National Service. I exclude the few who may be cheating the system by not actually learning Torah for one reason or another. The People of Israel is better off having learning going on in its yeshivot than having an extra 3000 troops a year. Without Torah, there is no Israel.
Shaffir to Herzog: Opposition failed to show leadership in political battles against PM (Haaretz)
from the article: Draft deferrals for yeshiva students surpass 50,000 mark in 2006