some people continue to download and install our HD game on phones that have 100MB of RAM and give us a bad rating... :)
Is there a way to limit app download to only sma
It's not one of the filters for Google Play as far as I know. http://developer.android.com/guide/google/play/filters.html
I guess you could:
Filter out devices that you know don't meet your criteria. You can do that from the Android Developer Console (just list the devices your app can run on and hit exclude to add them to the manual exclusion list). But given the number of Android devices out there, this may be difficult.
In-app, check the memory assigned to you and if not enough for a good experience, act on it. Let the user know (and refund if it's paid :) ) etc. This only if you're sure that memory is the only limiting factor.