And hee, I totally didn't realize the Bob-Tony similarities there, but given how Harry and Steve are both boy scouts in their own ways, they would need an arrogant, darker soul looking out for them.

Looking at some of my favorite pairings (to write or just to read), I think having a dark(er) character who needs light and hope and love brought into their life by another character appeals to me in general. In one sense or another, it works for Bob and Harry, Tony and Steve, Bruce and Clark, Neroon and Marcus, Spike and Xander, and Methos and Duncan.

It's not totally ubiquitous, but it's pretty common. At least I'm consistent? *g*