Transport is always a tricky subject in any game but for pokemon I feel it's a little more tricky than others mainly because if you do introduce things like a car? you would probably miss out on alot of exploring and to add to that you would only be stuck to a specific route making the game alot bigger than it needs be and having things in which are just totally unnecessary You see hints of what could be roads in Castelia City? but again it's just something totally not needed.
As for the rollerskates and Bike issue, I feel rollerskates would just refresh older players from the standard box set running shoes and the rollerskates would take advantage of a 3DS' 3d capabilities, the bike however I feel should stay in a game because it adds that adventurey feel to the game, I did really enjoy the Acro and Mach bikes in R/S/E as it meant that the player had to switch the bikes in order to get to certain places which were only accessible by one type of bike. Again this is something which I would love to see return in Gen 6, making area's accessible by bike only and making it so you need a certain bike to get there but it really isn't needed but more to make the game slightly more flashy.
This is a really good thread and I can't wait to see what some other people have to say on the subject!