actually retaining it could do just that. it is hard for developers to get their apps out if Google incorrectly flags a device as not compatible when it would other wise install and run fine. and Play Store doesn't offer a 'download apk anyway' option either. other app stores, such as the popular Amazon Apps doesn't offer such a filter and it hasn't caused any problems that i can see.
if the filter actually worked properly it might help things out. but as i can tell, 90% of the times my devices are listed as 'not compatible' it would sideload fine. the problem comes with paid apps. i cannot get NBA Jam onto my Nexus 10, or Real Racing 2 on it either, because Google Play won't even offer the APK to download, much less allow the purchase. it's not available on another market, and even though they'd install fine on my Galaxy S3, the APK can't be found under /data/app or /system/app. they apparently hide paid apk files in Android.
if one uses an older version of Google Play Store or the Android Market (which functions on older devices to this day, albeit in reduced capacity) the filter doesn't exist. but you cannot do that on any newer device running a current version of Android. the filter didn't exist in the beginning and nothing bad happened.