PITbull, you're agreeing with me more than you're disagreeing with me, believe it or not.
As I said above, a B6/F9 merger would make sense. (if the "benign" suggestion didn't do it for you, how about calling it a 69 merger? can I get you to at least giggle???) One reason it would make sense is that they differ primarily in the territory they cover, and thus would likely gain some economies of scale. The other is, as you noted, they will have trouble expanding into each others' territories because their products are similar enough that the newcomer will have trouble acquiring customers from the existing business.
Likewise, US could be modeled after HP, and the same thing could happen. If they expand in each others' direction, they will ultimately have little choice but to merge. But so what? It'd give them better networking, better coverage, and economies of scale. Not a bad thing.
I'm not against consolidation when it makes sense. I'm very much against consolidation for the sake of consolidation (which was, in essence, US's strategy in the 80s).
And even when the parties are an excellent fit, swallowing another business isn't an easy undertaking. Kelleher commented later on how painful the Morris acquision was...and that was an airline modeled in almost every way after WN.