While it wouldn't be great on the cabinets to live outdoors, if they are kept out of direct rain and moisture, and have decent covers, it shouldn't be that big of a deal. Yes, they will age more from living out in the weather to a degree. But, if you're doing outdoor shows with your speakers at all, they are already experiencing these conditions, plus they are taking on the wear and tear of being moved around all the time.
When I do outdoor shows, my speakers get covered with weatherproof covers from UnderCover NYC. They are acoustically transparent, so the covers remain on the cabinets rain or shine. And my speakers have been in rain more times than I can count, yet still look and sound good as new.
You can get outdoor specific speakers, but often times, the only difference is a weatherproof coating on the speaker cabinet. The components inside may be identical to the non outdoor counterpart.