Different expiry dates on H1B Visa Stamp and I-797

I received my H1-B visa stamp, the expiry date on it is Nov 2014 and the expiry date on my I-797 is Sep 2015. Is it ok ? Shouldnt they both be same. Shall I ask the immigration when i reach USA to put the expiry date on I-94 the same as I-797. Till when i will be allowed to stay in USA ?