It is amazing that so many people up here in the Highlands just go about their normal life in winter without four wheel drive, winter tyres can be a big help though.
If you are living very remotely, reliability is a major requirement, for the winter good ground clearance is a big help, along with suitable tyres.
Many Defenders (TD5's) have had starting problems up here when it's really cold, due to fuel waxing and the position of the pump/filter thingy (can't remember which but its positioned underneath the off-side rear quarter).
Diff locks, either factory fitted (Merc G Wagon, Toyota Land Cruisers, etc) or retro fitted, can be a real bonus.
I did have a modded 2001 Nissan Patrol, reliable with a rear diff lock, not as good as the older models though. I now have a Land Cruiser 80 Series, 4.2 td, 3 diff locks. Ultra reliable, brilliant off road and a great motorway/long distance cruiser. Half a turn on the the key and it starts first time every time, even as low as -20!
The heavier vehicles do have a disadvatage in deep snow as I found out when in the Patrol, trying to follow a mate in a Jeep Wrangler who had just skipped across the top, I just sunk in. This was partly rectified when bigger tyres were fitted.
If I had the lottery money I would get my Land Cruiser out to the guys at Arctic Trucks (
http://www.arctictrucks.com) and let them loose on it!