To me it isn't the season that matters, it is one's level of experience in those particular conditions. If you already have considerable experience in the kind of conditions you are going into, then I don't think it is unreasonable to go solo. If you lack experience, then getting that experience in a group is a better way, although you can also gain experience by going out solo but not going far. Doing your first snow camping solo 100 yards from the road is a good way to try it out, because you know you can bail if things go wrong.
But this kind of thinking does have to be left behind:
"Doing solo in the summer has its dangers but its usually only a few hours until someone walks along the trail ANYWAY so I figure if I get hurt someone will just find me on the trail."
There are plenty of places where this is a dangerous attitude in the summer as well, places where you need to be prepared mentally and physically and gear-wise to help yourself because no one is going to happen to pass by. Winter conditions just make that apply to more areas.
As to the mention of avalanche danger, yes, there are places where, under the worst conditions, it is not safe to go - solo or not. Being with a group affords some slight advantage - you might get dug out before you die - but frankly, it ain't much. Being in a group will not prevent your being caught in an avalanche, nor will carrying a beacon, shovel and probe. The only way to prevent that is by your choice of where and when you go. The safe choice is not to travel in risky terrain when the risk is high. Wait for conditions to improve or find safer terrain. Of course, the safer terrain may be no fun to ski, and that is one reason people are tempted to go out when they really shouldn't. So that is not dependent on being solo - it's a mtter of knowledge and judgement.