I think the main arguments against lawn/garden tractors are:
- Turning radius, maneuverability;
- Storage requirements, aka size;
- The blower may throw the balance of the tractor off;
- A higher percentage of the power is available for throwing snow with the dedicated units.
I have seen a couple of tractor units in use, one was a medium size Kubota while the other was a lawn/garden tractor of some sort. Both worked quite well, had a wide swath and seemed to get through the snow quite well. I was also surprised at how quiet the Kubota was, I don't remember much about the other unit other than it seemed to work, the one time I watched.
The Kubota also had a rear mounted scraper which could be use during the summer to level gravel and in the winter to pull snow forward so that the tractor could be backed over the pile and then make it go somewhere else. I have a hunch that unit was more than $10K new.