Well, they are nearly the same thing. Service Packs have not been a common term with Dynamics CRM, Rollups seem to be the one that's used almost always. What I have seen from my personal point of view is that Service Packs tend to have a lot of stuff
in them, meaning they bring about a overhaul of the existing system, introducing some major new features, integrations, etc. Rollups on the other hand tend to "fix" bugs more and sometimes come with new additions, for example the metro look of CRM, etc.
The difference is very little, but the word Service Packs tend to sound big compared to Rollups. :)
Admin QuikView Solution for CRM 2013