I'm just a little confused looking at the show notes. The AM2 supports the Sempron but the AM2+ does not?
Socket types on the mother board
Yes, as far as I know this was the case. I think the AM2+ was not the most gigantic change so support for it required a change to the BIOS on the AM2 Motherboard to get it run but it was possible. I believe that AMD went ahead with the next generation development without trying to make AM2+ a focus so it's very possible.