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No,it should have no affect. I believe that the BT Homehub is capable of more than 50 metres at least.
They are just trying to confuse you. Almost all wireless adapters use 802.11b, g. If you are looking at playing online then I would recomend you to buy a 802.11n as they are 'the new generation', other wise if you just want to browse around on websites you should be fine with either a 802.11b or a g.
Just a bit of background information if you are interested. The 802.11g is faster than the 802.11b. The 802.11g offers up to 54 megabites per second while the 802.11b only offer 11Mbps.