If there would be no service packs, then the possible ways to grab all the updates would be from Microsoft Download Centre or otherwise the Windows Update feature of the operating system. For people who keeps their Windows Update settings to Automatic may not encounter any significant issues but for all others, identifying any new release would be a challenge if they don't put a check on it frequently. As such there will be every possibility that they might miss out any of the important updates through oversight.
Microsoft has already rolled out few updates for Windows 8 which includes a General Availability Cumulative Update on 9th October that brings around a number of improvement in the power efficiency, audio/video playback, compatibility of apps and performance of start screen apps. This KB2756872 update wasn't by any means a smaller release and has already caught the buzz in the popular social media.
With such updates made available at an early stage, Microsoft aims at keeping the operating system up-to-date and running with all latest and stable features. With these availability, it is also an attempt to convince the business users not to wait for service packs for testing and deploying new versions of their software products. New Windows 8 Apps update are also heading to the Windows Store while few are already listed.
So whether Windows 7 Service Pack 2 and the first service pack for Windows 8 would come or not, smaller updates and patches would keep rolling out and all that's good for now is that you won't feel abandoned after purchasing and setting up these popular operating system. Microsoft has still not responded to any of these news (or rumors) and hence it will still be too early to predict anything in this connection. In case if there would be no service pack for Windows, third party apps will continue to offer them packed into a single standalone installation file for all those Windows users who likes to manually update their systems.