It'd be interesting to know what proportion of their revenue the Asset Store accounts for. My own guess is very little compared to the revenue from licensing Unity itself. When a 20-person company licenses Unity Pro with iOS/Android support and the Asset Server, that's either $100,000 in licenses up front (plus upgrades later), or $2450/mo for the subscription option. And there are quite a few companies that size (not to mention bigger). I would be surprised if Asset Store revenue is really rivaling that. Hence my guess is that the free version of Unity is mainly intended as a "freemium" product to drive later sales of the Pro version.