These places are completely leapfrogging desktop technology and going straight to mobile. It isn't just the case that the end user can't afford desktops: think how much infrastructure is needed (in terms of power, connectivity, etc) for a desktop device versus a smartphone or tablet.
Not sure what you mean by connectivity -- desktops and mobile devices have the same options: wireless (3/4G, etc), and wired (via wifi for the mobiles). A desktop surely doesn't require buildout of a infrastructure-heavy wired network to have comparable connectivity to a smartphone.
As far as connectivity goes: again, you're talking about a hypothetical. While there's no reason you can't create a low-bandwidth experience on desktop, the fact remains that simply opening my email transfers over .5MB. Opening my Facebook account transfers more than 1MB. Doing this on my phone uses a fraction of this data.