If you commute it can be Blue Bird weather in the AM and raining when quitting time rolls around, a commuter bike w/ full fenders and a cheap rainjacket stashed are well advised unless one wished to call for mommy-van-rescue.

I don't have to maintain a structured training schedule anymore so going out into a deluge on purpose is not going to happen.
Often it rains overnight and the roads are soaking wet, as this AM.
My winter/wet bike w/ full fenders made for a pleasant ride w/ no discomfort or time consuming clean-up.

Taking a page from traditional British club cyclists and riding a machine that will accept full fenders and carry enough stuff for a self supported weekend tour at pace on secondary roads makes sense for many recreational riders. That design is sadly lacking in most modern machines today. Instead of asking "How light?" ask "What size tires fit with full mudguards installed?".

-Bandera