I'd have zero problems with hiding the first 72 hours, especially for publishers who want their launch day sales to look mostly accurate. At least that has a purpose relative to the platform.
This is a great solution to both "sides" of the issue. Publishers worried that their product will be viewed poorly during the most critical period (first launch), and users/devs that want to see data on a game's ownership.
SteamSpy won't have to continually field requests about games numbers that haven't had a chance to be anywhere close to correct. The site freely admits the data is not useful until more time has passed even. Seems like a compromise solution if the publishers continue to throw a fit about this data being out there. If they really really don't like it being out there, they should be talking to Valve not SteamSpy/Steamcharts/etc.