Whether or not you actually volunteer has absolutely nothing to do with the five-year limit.
The limit is based on the type of orders. The navy will normally cut most orders as invol for that reason, even if you verbally "volunteered".
Also there are many, many exemptions from the five year rule...all contingency and title 10 recalls are exempt IIRC...ie they do not count against the five year limit. With GWOT ongoing, it would be pretty hard to get ANY orders which would count...it would have to be ADSW doing something totally unrelated to GWOT or contingencies.
Check out the USERA web site.