Ravi, to be 100% clear, even if you have the same vendor APs and are using PSK, a wireless client will still have to re-authenticate every time it roams (generally takes about 40-60ms). The only way to help this process is to enable one of the 'fast' type roaming protocols. (OKC, FT, PMK).
If you are just using pre-shared-key authentication (PSK), the roaming process is pretty quick. It's normally not a problem and happens quickly enough that users don't notice.
When this re-authentication CAN be a problem is when the client is using a time-sensitive application - like a voice call and using 802.1X authentication. If it's using PSK instead (no 802.1X), this MIGHT NOT be a problem. But if it's using 802.1X, and there's no fast roaming protocol being used, then most certainly the re-authentication process is going to be disruptive to the voice call. The 802.1X authentication process will generally take 500-750ms...which is far too long a time to be acceptable for disruptive voice calls. The majority of that time it taken by the during the .1X/EAP frame exchange.