Yes, I've noticed it with the woodwinds too. It seems impossible to create a natural sounding vibrato with artificial parameters like LFO pitch and filters, it has to be sampled. I don't know exactly how (or if at all) Yamaha has implemented this in the SA2 voices. Roland certainly wanted the tones to be flexible so that the player can decide if and when a vibrato comes in or not, which is not possible with the basic sample having the vibrato in it. It would have to be a kind of scripting so that a sample without vibrato would have to blend into a vibrato sample e.g. when applying aftertouch without the switch of samples being audible in an abrupt way...