If he's in say, Redmond or Issaquah (especially the latter), where some of the MS campuses are, biking every day all year becomes less viable. There's no way I would ever bike to work in Issaquah even if it was a reasonable distance, because you spend too much of the year getting pounded by rain/snow in cold temperatures, or subject to high winds.

I do agree about Seattle proper, though.

EDIT: For reference, Gates' home is in Medina, WA, near Redmond. It appears to lie pretty close to Lake Washington, so the weather is PROBABLY relatively similar to Seattle, but it might be more unpredictable since it lies further inland...

Do you perhaps live somewhere fairly arid? Even so, I think it's still all about location.

25C is regarded as very pleasant weather here in the southeast US - a nice early spring or late autumn day. :) Humidity is generally in the 80%-90% range when the weather is warm, and from mid spring to mid fall the temperature is generally ranges from 30-35C and sometimes gets up to even 40C.

In that kind of weather even a brisk walk will leave you drenched in sweat and you wear out very quickly because your body can't cool down, since evaporative cooling doesn't work. The temperature alone isn't bad at all - I've spent time in SoCal when it was ~100F - it's the humidity that gets you. Nobody bikes to work here - you'll sometimes see bicyclists on the road but for recreational purposes. I think it would be a fine thing in winter, but my commute is 35 miles of open highway.

So I end up going to the gym and doing a lot of yardwork. I'd like to include something like biking to work in my routine, but it's just not practical for me right now.