Musing on seasons

I don't remember the last time the contrast between two seasons so stark.  On Saturday I ate ice cream outside with my girlfriend in the warm sun, beneath a deep blue sky with pretty clouds that I would have liked to stare at and find shapes in -- a perfect summer afternoon, if only I didn't have to spend the evening at work!  Sunday, the first day of fall, was chilly, gray, and damp.  I kind of wish the sans always did this, so that the solstices and equinoxes would actually mark the transition of seasons like they're supposed to.  Fall doesn't usually really come until October, and March is such a messy month that I don't think any season can properly lay claim to it.  Winter obviously comes well before the middle of December, and Summer well before the middle of June.  I'm tempted to think the solstices should mark the middle of winter and summer, rather than their beginnings.  Then again, the changing of seasons differs from place to place, so there isn't really a universal date of their beginning and end.  So why do we say that's what the solstices and equinoxes are?