Well, I'm sure the casting people did an exhaustive search, and I'm sure San Francisco audiences aren't
complete backwoods hicks to be taken in by... whatever.
I would suggest that perhaps the first cast people see is the cast that sticks with them, and it can be hard to accept other people in the roles. Especially when compared to people briefly seen on the television.
In the end, you like what you like, and maybe the OBC is this shining star that can never be attained by another cast. It's possible. I haven't seen them, though, and I liked the SF cast just fine.
'"Contrairiwise," continued Tweedledee, "if it was so, it might be; and if it were so, it would be; but as it isn't, it ain't. That's logic."'
~Lewis Carroll