The surges in today's wars are only limited for political reasons, and the only reason that's happening is because people in the military want to avoid another Vietnam. If Vietnam hasn't happened yet, the military isn't going to be thinking in the same terms politically, and are going to do what they did OTL, which is to keep demanding more and more troops.
Besides, an Iraq-style surge wouldn't have worked in Vietnam, just as it isn't working in Afghanistan. Divide and bribe doesn't work as well in national liberation struggles.