20 miles each way is 2 hours total for a very fit cyclist. It's 3 hours or more for most people. And you'll need a shower when you get to work (and home, really). I don't think that's convenient for most people.
2 hours total yes, which is enough to maintain a reasonable level of fitness. You don't need a shower when you get to work if you wear lycra - it's fast wicking and you'll arrive drier than if you had taken public transport in cotton.
Also odour is caused by bacteria. If you shower before leaving and wear clean lycra there's no need to shower again at the end.
2 hours total is not a reasonable level of fitness. That's an exceptional level of fitness that would out you well outside average. Most people cannot bike 20mph for 60 minutes, or anything close.
As for not needing a shower, I'm wondering if you're the stinky guy at work. An hour of hard exercise will make anyone sweat. Wicking clothing will help but not eliminate this. As for the bacteria, those are on your skin. They reproduce constantly, and showering beforehand will not change that. You need a shower afterward to clean off the ones that have grown on you during your 20mph bike ride. You at least need to be taking a "sponge bath".
