In Apple's case, the more secure options would either be "an app must include a perapproved list of which other apps are authorized to see that it is installed", or popups for permissions like "Image Editor wants to know if you have Dropbox."

Since Apple has both the authority and the manpower to approve or disapprove of apps, they chose to not take either and to stick with the version that gives the best user experience, while also allowing devs to continue checking installed apps when they need to as appropriate for cross-app interaction.

I guess it sucks from iHasApp's perspective, but I don't have any more sympathy for them than any other spyware developer. Just because Win32 apps aren't sandboxed and can read arbitrary data out of my home folder doesn't mean it's an OK thing to do.