Is there any real difference (to a baby) between sippy cups w/ latex/silicone and regular bottles?

My son is almost 10 months and has been drinking from a sippy since he was about 7 months. He seems much more comfortable w/ the sippy cups that have the silicone/latex . If I give these to him, it doesn't seem to bother him not having a bottle. I'm uming that it's b/c they are alike, but then my question is why get rid of the bottle anyway? All he really needs to know is how to hold the cup...right? Not necessarily what the texture of the spout his drink is coming out of...or am I wrong. I understand the point is to get them off formula and onto milk once they are a year old, I just don't get why he shouldn't have a bottle if his sippy is basically the same...just a different shape. Can anyone help me?