There are at least a few good reasons I can think of to change your exercise with the seasons.
1) It prevents us from developing overuse injuries and allows our bodies to recover. Even if you're not an athlete, your body will thank you for changing things up, but make sure you go into the change slowly as your body adjusts.
2) It makes for a better, more capable body. You don't want to get good at just one thing, you should want to be proficient in various different activities and aspects of fitness. This will make you more adaptable to whatever life throws at you.
3) It's just more interesting to learn and challenge yourself. Nobody likes getting bored and changing your routine makes sure you are staying mentally checked-in during your workouts.
4) Working on one aspect of your fitness can make other aspects better. Just like losing weight can make you a faster runner, getting stronger and more flexible can help nearly any activity that you do. Think about winter as your off season. What do you need to get done to hit the ground running when the warm weather comes back?
One of the best things I've ever done for my running is to stop running. Despite running a marathon in under 3 hours back in 2013, my right ankle was always really stiff and always bothered my when I ran. After I ran Boston in 2014, I took about 2 full years off of running and started focusing on body weight exercises and movement I learned from attending Anatomy in Motion and Animal Flow workshops. These two disciplines have made me the strongest and most flexible I've been in my life. Much to my delight, when I went back to running this summer, my right ankle stays much looser and I am able to put it some really good paced runs despite my lack of running. So 2 years is longer than one winter, but the principle still applies.
So now that the weather has changed, don't fight to try to keep things the same. Embracing and shifitng with with weather can be a much healthier decision. You don't have to go cold turkey and you can still do some of you summer activities, but you should cut back quite a bit and replace it with something else. Start taking a group fitness class, train with weights (staying off the machines), start stretching more, walk/hike outside instead of running (walking is good all year round, but it is best done outdoors), learn to cross country ski or snow shoe. This winter, I plan on replacing most of my running with cross country skiing (if we get the snow for it) and focusing back on Animal Flow and Anatomy in Motion stretches.
I do realize in writing this that there are a few die hards that don't want to give up routines (typically a runner or a cyclist) and to them I say this. If what you are doing now helps your body feel good, keep doing it. However, if you have a few problems, aches, and pains, please make this into an opportunity to help yourself.
If you are worried about starting something new or outside your comfort zone, find a good physical therapist that can help you navigate through all your questions and address any concerns either of you may have.
A little from Dr. Dan, a little from Lisa but always a lot of good stuff!