No one who uses dial-up wants to use dial-up.
But the modern web is hopeless on slow connections. Some sites are pretty bad even at standard cable internet speeds. Site developers who work with gigabit fiber connections should try their pages at 10Mb or slower and 3G speeds out of courtesy to the real world.
The copper cable bringing ADSL to my house broke and it is prohibitively expensive to fix. I haven't had this bad Internet connectivity after 1999 but I can still work alright with mosh + tmux. Browsing the web isn't very nice, though.
I regularly pull 60/30 speeds on LTE. Broadband is 50/5. :)
As I said - if you'll actually look data in aggregate, you'll notice that people love to use their mobile devices for reading the web on commutes. Millions and millions of people devoting their morning/afternoon commute time to reading the internet on their mobile devices and mobile coverage in those conditions is nowhere close to "universal LTE without packet loss". A lot of cities (heck, even CalTrain in SV) have spotty commuter line coverage, especially when cells get loaded due to large amount of clients. Those people will then get crappy experience if you just assume everyone has LTE.
Is anectodal feeling data really how you design and optimize your software for end-users? :/
In particular, the latency can make your browsing experience rival dial up.
yes, 2g isn't dialup modem speed, but it isn't useful, either