Well from what I know the main purpose of the software updater is to make sure most of the important software installed on a computer is up-to-date because the updates contain patches to fix security exploits etc.. Most of the software that release these 'minor' updates will not release a major version unless it contains something 'big'.. They wont release major versions regularly, only small patch updates and if the software updater wont pick up those updates, it doesnt serve the purpose.
Dont get me wrong, i LOVE this new feature, just hope that it could be more effective.