I live by 3 PAB's, and I still spend more at BrickLink, but if it wasn't for the PAB's I'd spend even more. Let's say there was a PAB online, I say it's safe to assume that the PAB online would have a selection as good as the one at LEGOLand California, if it's online, and TLC is running it, it shouldn't be out of the question. So, with that well stocked of a PAB with rock bottom prices (price for a pair of black minifig legs at LEGOLand's PAB is 2.5 cents, on BrickLink it's 20 cents), most basic bricks and whatever special elements they have will be purchased there. So now BL is just used for specialty pieces and old pieces. Which isn't too bad. Except for the fact that small stores rely on the sales of basic bricks. That's their bread and butter. Let's face it, buying 3 specialty pieces of 40 cents each won't cut it. So they can't compete with the big stores even more. Big stores will start charging more for specialty pieces because they have to make up for the loss of parting out a set and not being able to sell those basic bricks for how much they were getting before. An online PAB would be just like LEGO opening up a BrickLink shop. Selling at the lowest prices because they make the stuff. Being very trust worthy for new buyers because they are LEGO. Who can compete? It doesn't matter how many sets of 7998 a store parts out, because when LEGO needs more, they call up the factory floor and go "Hey! We need more tan 1 x 4's!" End of BrickLink.
I'm not saying an Online PAB would be bad for us. Heck I'd save cash on gas. But I know for some BrickLinkers, it will hit close to home.
Just like you all are saying now, even if for some reason TLC charges more for their stuff, you won't seem to mind much.