I guess you can apply the 48dp grid to older android apps as well. The grid is not about android version, it's about screen sizes and resolution in my view.
Yes it works, "dp" are meant to be of the same physical size on all devices (even though there are badly implemented firmwares where it differs). What I mean is - these best-practice sizes should somehow be implemented (On ICS, buttons seem to have a min-width of >= 48dp per default - but there also ought to be layout helpers for spacing etc.).
