I always thought the idea there was that a website needed to grow organically before google would rank it highly, which makes sense to me. Prove yourself first by building a network, they aren't obligated to help out.

The difference here is that the play store is the one and only way to get apps for a regular user. By putting that banner up, they're discouraging anyone from trying it even if they found out about it through other channels.

The analog in 2000 or so would be if Microsoft added a warning banner to any website you visited in Internet Explorer with a low link count.