Question regarding Petition Validity Date

Recently, my H1-B petition got approved. I have a question related to petition validity date.

On I-797 form, it is written petition is valid from Jan 2013 to Dec 2013. Though, my petitioner has filled it for 3 years. In I-129 intended length of stay is written 3 years.

Now, questions is does it mean my H1B issued visa would be valid till Dec 2013 at the most? After Dec 2013, I've to fill the extension else I've to go back to home country... Right?

What is the role of I-94 in US? Person may have different date on I-94, other expiry date on petiition or VISA

Yes, the visa will be issued for the same duration as petition validity. Once you are in US and your petition is about to expire, your employer will have to file for extension. Once approved you can continue to stay and work and don’t need to go for immediate stamping.

If the extension is not filed, or is denied then you will have to return to home country.

I-94 is issued at PoE (port of entry) when you enter US. Its dates are also dependent on the petition, and you will receive it until Dec 2013. When the H-1 extension is approved, it will be accompanied w/ another extended I-94 valid until extended petition’s expiration date.