http://thegenesisblock.com/mining/ to help figure out costs and return... my question is are the statistics on that site calculated based entirely on the assumption of solo mining?
It does not matter for cumulative return, but in practice - forget about solo mining. No one should mine solo unless you are in control of at least 1% world's hash power. Otherwise it is quite possible you mine your first solo block when block reward will be 12.5 BTC or even 6.25 BTC, or simply put - never