Although the op has every right to get miffed at what happened with him, i cant help but feel that samsung is not totally at fault here. The i9100G and i9100 both, are afterall Samsung Galaxy SII only & as such they are expected to be marketed as same. Consequently the retail box & package will also be identical as they are in fact SGSII only. Now the op could have prevented it by buying from a local store where he could have inspected the box. In the box where the date of manufacture sticker is pasted, there on the top of the sticker itself the model number is written. With adequate research one can be aware of the model no for both G as well as non-G.
Now coming to the issue of the G having a inferior SOC compared to the non-G, well it is actually not true. The cpu part are basically the same as the Ti OMAP 44xx and the Exynos/Orion 42xx both have a dual core ARM A9 with neon vfp instructions. However the G model does have a noticeably weaker GPU in the form of SGX 540 (Although till the Mali-400 or the SGX 543+, it was the top dog in mobile GPUs).
However one should keep in mind, that the upcoming Galaxy Nexus has the exact same SOC as the G & it is widely accepted that it is no slouch in terms of performance. Regarding the original development scene, the G does not have too much love from the development community simply because it is not available widely & in most territories. AFAIK, the G is only available for sale in the asia-pacific region only. But on the bright side, expect the development to pick up on G as soon as the devs manage to successfully port ICS.
@Op, dont be too disheartened, you dont have a faulty kit with you, rather a different one. Although you can continue to be angry & rant about this, its better if you simply accept this fact & move on. People like me who have the non-G version have faced other issues, which TBH are much more pressing & disappointing. Just enjoy your device & show it some love.
Apologies for the long post