I think it is really subjective and about the "long tail" of apps. If I say that OmniFocus locks me into the Appleverse, someone else will mention an Android-exclusive app and we'll (objectively ;)) discuss for hours. Carcassonne and Anthill may not have worthy Android ports, but I'm probably missing out on Google's best-in-class maps.
The shopping experience may also have a lot to do with each platform's perception. The Play front page[1] looks absolutely uninviting to me. In iTunes or on the iPad, I usually scroll around and discover apps by topic. What do I do in the Play store if I know all the front page apps already (not hard)?
[1] for those of us who are abroad: http://webcache.googleusercontent.com/search?q=cache:https:/...