I can certainly see where an FEL would take a lot of weight off the rear end making a 4wd more effective.
Owning and actually using a 4x4 diesel truck, I can also agree with that comparison, but I will say that there is a noticeable difference. Unloaded, the rear end of a pick up truck is extremely light making it difficult to get good traction. Most of the time, when using a tractor, the chore itself puts MORE of the load on the rear end. The comparison is valid though. As Tudor alludes, the operator has to understand the limitations of the equipment AND the environment. I've had 2wd trucks stuck more than once, but it's always been pretty simple to retrieve them. Take a 7,400 lb truck, load 5K in the bed, and then burry to the axles. Now that's STUCK. Even after unloading the bed, we stood an 8N on end repeatedly trying to yank it out. When I get that truck stuck, I always know it's going to be a real job getting it out.
So it sounds like both will do the job, but the 4wd can be pushed farther at the risk of a major OS moment if you exceed it's threshold. 2wd can be modded (Ballast, chains) to increase its performance, and under some circumstances this increased performance will exceed what a stock 4wd will do. 4wd can also be modded in the same way, but often times the increase performance will only get you a LOT more stuck.
I've been looking at tractors for YEARS now, and would LOVE to get into a 20 to 25 hp 4wd machine with a FEL. Problem is that the absolute bottom end on price for a used one is in the mid $6K range. I occasionally see one for a little less, but not very often, and usually they are in the $7K and up range. Conversely, 2wd models seem to be almost half the cost. 2wd machines with a FEL in this size range seem to sell for less than $4k. Even seen some go for noticeably less. So the root of my question is really trying to understand what I'm getting for the extra money spent. If I had some acreage, I would think that a 25hp 4wd would be bare minimum. I'm on 1.5 acres, and I use a ZTR for mowing it. I use my ATV to deal with snow, and I may end up with a plow on my truck at some point. I'm repairing its replacement now, but I'll be keeping it for "farm" duty. I have a close friend who lives about 7 miles away and he has a nice skid steer, so if I NEED to do heavy work with a loader, "I know a guy". Most of my uses involve my garden, getting a machine into a location that I can't get a truck, or provide a more effective means of lifting/moving heavy objects. While I really, really, really want a 4wd machine, I'm still not convinced that the benefit is worth the substantial increase in cost. Seems like a properly equipped 2wd could fit my needs with room to spare.