Definitely not best selling computer of all time
Wasn't the Commodore 64 the best selling computer of all time?
The iMac G3 only shipped for four years or so, and while it did well, it was only occasionally the best seller in that period - that itself an unfair comparison against a fragmented PC market - a huge market that made Apple look like a true minority player by comparison. It is ludicrous to claim that such a minority interest machine could have made a significant impact on uptake of the internet.
It might have give a little push to consumer enthusiasm but if it hadn't been around another machine would have served just as well. I remember internet cafes stuffed with these, but far more were stuffed with beige box PCs.
It was a decent return to form after the terrible era of the "LC" but felt cheap and nasty compared to old style Macintosh boxes; the keyboard was mediocre and the mouse was horrible cheap tacky junk.
In that same era IBM, Toshiba and other business laptop manufacturers were selling internet ready Windows machines that you could just turn on and go with, so I don't think Apple have any special claim to accessibility there either. I can't recall when the awesome T40 released, possibly after the G3, but it would be no surprise to me if the T40 series alone outsold the G3. Now there is a machine that is worthy of praise and memorial. I bet there are more people still using their T40s than are using their disposable consumer toy G3s. I still see T40-43 machines for sale at fair prices, while old plastic iMacs are dumped at the side of the road for hard rubbish collection.
Perhaps somebody has some figures?