Gmail's slow connection message is great, but it's there because Gmail is a multi-megabyte app that will take a long time to download if you're on dial up or something. That's a bandwidth issue rather than latency or line quality problem. None of the points I made say anything about bandwidth.
I completely agree with the point you're making though; if a user is on a low bandwidth connection then sending as little data as possible is best, and that's likely to be plain HTML with very little rich content like images.
That said, Gmail's slow connection UI is horrible to actually use. Very few people choose it over normal Gmail. Most people want the big fancy app, so we as developers should work out the best way to deliver that.
I completely agree with the point you're making though; if a user is on a low bandwidth connection then sending as little data as possible is best, and that's likely to be plain HTML with very little rich content like images.
That said, Gmail's slow connection UI is horrible to actually use. Very few people choose it over normal Gmail. Most people want the big fancy app, so we as developers should work out the best way to deliver that.