Yes they are very very different, and yes all Siamese are this way coz they are soo intelligent,they need constant stimulation but their isn't another breed imo like them except Ori's-Moggies are at one end of the scale and Siamese are very much at the other end
Moggies again imo tend to respond and Siamese will react in context to a situation or conversation
have a look on youtube and see if you can find some clips to give you some idea