I hate cycling...

not trying to call you out, but for the sake of conversation, i don't believe you're riding 50 mi a day, ONLY because thats like 4 hours start to finish... including shower and everything, i mean.... and who has the time for that?
You make time. You make time to do things you love... or perhaps because you've got no other option.

I know someone at my previous work that cycled from watford to motspur park... and back. Every working day (well he was an off shore engineer so every so often he'd be stuck on a boat in the north sea... but the rest of the time). google maps the distance I don't know what it is, but it's massive.

My dad also used to commute to work and it was over 20 each way... in seatle... they've got hills there...

Neither could change where they work or where they lived and it was their chosen method of transport.

I do a measley 30 miles a day (although, unlike the two above, fixed, sometimes on polo bike, also I think in worse traffic) as I've said before it's what you are used to, when I was a kid I thought 4 miles was a massive bike ride, ten years ago i'd say commuting 10 miles each way was insanity, when I last changed job I thought I'd only cycle in every other day. Now I wonder if there is actually a limit on how far one could cycle on a commute once you get used to it?

edit: also your maths is wrong, on a lovely geared bike in rolling kent country side I'd say he'd be taking about 2.5 hours to do 50 miles, if it's a commute he's doing two legs of 1 and a quarter hours... not too much at all... I know people who's train/tube commute is way longer than that.