Do we even need another service pack? Other than rolling up updates I'm not sure what purpose a SP2 would serve.
Meanwhile business customers would be elated to not have another SP. Service packs break their precariously programmed software, and their vendors aren't about to support a new service pack any time soon.
Windows service packs are generally just compilations of patches released since the last service pack, most of which the majority of companies are probably installing via patch management utilities anyway. So the argument that a service pack "might break x, y, or z" may not be the best argument since you figure most of these patches are getting applied anyway.
On the other hand, sometimes service packs DO contain new functionality (like Windows XP SP2) which was not included in a previous patch and those can cause quite a bit of issues. It is clear that MS won't be adding features to Windows 7 via SPs in the future, so I really don't know what harm it would do do release a cumulative patch update once per year even if they don't want to call it a "service pack."