Dragonblade, to me it seems the biggest source of frustration is that you're looking for rational excuses from "Bob" why he doesn't want to switch to 4E, so that you can counter them, but it's pretty clear from what you've posted that "Bob" either doesn't have any rational reasons or he just doesn't want to give you any so you can counter them. Maybe he's made a subjective decision based on personal preference; you're not going to convince him otherwise, and to continue to try will just force him to dig in his heels even more, and he may end up resenting you for it.
You see this as a 3E vs 4E issue, which you think can be discussed in a rational manner, but really what it boils down to is a matter of personal preference, which often can't be rationalized.
Here's a couple examples to illustrate my point.
I love olives -- black olives, spanish olives, they're all good. My wife doesn't like olives at all. I can't imagine anyone not liking them, because to me they just taste great, yet she doesn't like them. No matter how much I might try to tell her how good they taste in salads, on pizzas, on sandwiches, by themselves, she's not going to eat them because she's already decided that she doesn't like them. It's not something we can rationally discuss, because it's based on personal taste. I ordered pizza a few weeks ago and forgot to specify no black olives, and I sat there watching her pick them off. I was thinking, "It's only a few olives, just eat them already." She was thinking, "I hate olives and don't want them on my pizza. Did I get them all off yet?" If I did try to force her to eat olives, she'd get mad at me and we'd have a big fight. Plus she'd probably make sure I never get to enjoy olives again. As it stands, I leave her alone about it, because she doesn't like them, and every once in a while she remembers to order a pizza with olives on half or she picks up a small jar of olives for me to keep in the fridge for pizza and salads.
Another example, closer to the current topic: I have a good friend who really really wanted to find a girlfriend who was a gamer, but the girl he fell in love with wasn't a gamer. She had no interest in gaming -- though incidentally her interests include a lot of things we normally associate with gamer interests, like fantasy fiction, Manga, etc., and she loves all things vampire -- though she understood how important gaming is to him and doesn't begrudge him spending time on gaming. He tried to get her to try gaming a few times, but that always ended in a fight. Not fun for either of them. He'd say, "But you like Buffy. You like Heroes. You like this or that; you'll love gaming." She'd say, "I don't want to try it." He tried inviting her over while we were gaming, so she could see how much fun we were having and want to join in. She'd sit there on the couch while we gamed and read a book. He tried telling her that Vin Diesel is a gamer; hey, if it's good enough for Vin then it's good enough for anyone, right? Still, she wasn't interested. I told him to let it go, my wife told him to let it go, but he was still having a hard time with it. Finally my wife told him, "Look, if you force the issue she won't ever want to try; in fact, she's likely to associate gaming with you nagging her and come to resent gaming and the time and money you spend on the hobby." So he finally accepted the fact that his girlfriend wasn't going to be a gamer, and he learned to let it go. At least his girlfriend was supportive of his hobby.
Fast forward several months; now they are engaged. One night during a gaming session -- she still comes along with him and sits on the couch reading while we play -- she makes a passing remark that Ravenloft sounds interesting and she might give gaming a try if another member of the group was running a Ravenloft campaign. So my friend goes out and buys the Ravenloft hardcover for our other friend to run, we roll up characters for it and we play a few sessions. She seems to enjoy it, so we have a sporadic Ravenloft campaign she plays in.
The point is, she had to decide on her own that she wanted to give it a try, and no amount of "convincing" on his part was going to change her mind. It would have had the opposite effect.
It's not irrational to not want to participate in a discussion about things you hold strong feelings about if you know that the other people in the discussion also have very strong opinions that differ from yours. At the end of the discussion it's highly unlikely that one person is going to say, "Your reasoning makes a lot of sense; I'm completely changing my opinion on this one." It's even worse if he knows he's the only guy who feels the way he does, so he may fear that any discussion on this topic is likely to end up with everyone else "teaming up" against him.
So my advice is to let it go, and either he will decide to switch to 4E to continue playing with you guys or he won't, but nothing you say or do is likely to change his mind at this point. Just give it time, keep being friends, and in time anything can happen.