This can be a useful service if he's providing checks that aren't present in the plugin, but I think it needs some changes before it can be useful as a user-facing service. If the target audience is theme purchasers, the vast majority won't be able to judge the merit of any particular error/warning, so they'll need a lot more hand-holding on what really matters.

Theme Friendly's format has more potential as a user-facing service. It provides separate scores for errors and warnings, provides a manual review score, and lists features separately so that missing features aren't interpret as "problems". It also has a section where issues can be explained. This requires more work, though, so it's not as simple as an automated scanning.