xD I guess it makes sense to have an extra seal on the turbolifts - to help preserve the ship's atmosphere if there's a hull breach. An airlock's a great way to deal with decompression, contamination, even radiation leaks, which is good since the turboshaft runs through basically the entire ship.
Who else was impressed by the new movie's scene of Spock boarding the turbolift in the shuttlebay, then emerging on the bridge - with no visible change of camera angle or switching to a new scene? It was seamless, so either a neat physical effect - with the turbolift prop standing right between the two sets - or else it was a very smooth computer effect. Either way, rather cool.