Seems to be some questions about h3 and Qc1. I don't know the reasons for these moves either. Just some vague observations, with no supporting analysis
1) Markovich gives 17. Bb2 c4?! 18. Nd4 cxb3 19. axb3 as good for white. If that is true, then it seems that part of the reason why black covers c6 is because after ...c4 white has Nf3-d4-c6. If white doesn't play h3, maybe black can just play Bg4xf3, when there is no reason, in the short-term at least, to worry about c6?
2) Another idea (or maybe in addition to (1) above) is that maybe the f3 knight is just a better piece than black's light-square bishop. For example, in Flear's main line when the bishop goes to d7, it's basically a defensive piece. But the f3 knight could find some good squares (c4 or d4), and/or help in an attack on black's king.
3) My idea on 20. Qc1 is that maybe it gives some additional attack possibilities for white on the dark squares around black's king. Flear's main line seems to indicate this, since black spent 3 moves (20. ...Qa6, 21. ...Qc8, 22. ...Qf8!) to cover them.
4) Also, and not related to Qc1 exactly, but it seems like the moves 18-23 were for the most part defensive. 18-19 black repositions his bishop to cover c6, 20-22 he moves his queen to a defensive role on the kingside (as a response to Qc1, maybe, but I don't know for sure), and then on 23 plays Ra7 (getting the rook off the long-diagonal). To me, this seems to imply that there are some neat tactics lurking somewhere underneath.