Owners of the Samsung Galaxy S2 will not be getting the update to Android 4.1 Jelly Bean due to hardware limitations as it lacks components that would be needed to run the OS smoothly and efficiently reports CP. The Samsung Galaxy S3 on the other hand will almost certainly get the update.
No Android 4.1 Jelly Bean for Samsung Galaxy S2. Yes for S3
It is thought that some of the limitations include the screen resolution which is on the low side. The majority of Galaxy S2 models come with a screen resolution of 800 x 480 and have a dual core chip. Quad cores are the preferred choice for Jelly Bean if not dual-cores with new architecture. It is also thought that the new Android build does not play very nicely with the Touch Wiz interface, hence making it more complicated for older Samsung models.
We saw something very similar when Android Ice Cream Sandwich was launched last year with the Galaxy S I900. Samsung said at the time that it would not get the update due to limitations with the hardware along with incompatibility with other software running on the phone.
It is believed that Samsung will be revealing the list of handsets that will be updated to Jelly Bean 4.1 very soon, right now the only handsets that we know for sure that are getting Jelly Bean are the Samsung Galaxy Nexus, Nexus S and the Galaxy S3.