I think web based start ups could be massive in the under-developed world. They don't have the infrastructure as more developed nations. Look at Estonia they have moved most of their infrastructure online and its working well for them(well if you discount the russian cyber attack a while back). The problem for these countries is internet access but there are lots of pretty cool projects giving them access. Also with open source development tools wide and the low computing power needed for developing web apps the barrier to entry is a lot lower.

of course if anyone from these countries applyed and they had something that sparked interest they would be invited over to YC interviews. Its not that different than me applying from the UK.