Honestly, I would have agreed wholly with you until I spend 1 month volunteering in Kiribati. 2/3G is the norm there and even few KBs would make a difference. It reminded me a lot of my childhood with 28/56k modems :/

Additionally, I believe countries like India, Pakistan, Bangladesh, ... are in similar situation infrastructure wise (please correct me if I am wrong) and so for 1/2B people would benefit from a slimmer web.