I think there are a few differences here that are important to note.
1. When I buy yard equipment, I look at the engine. Too many of the cheaper brands are skimping not only on the sheet metal, but the engine as well.
2. Especially true with Mowers -- sheetmetal is a huge problem on the cheaper equipment. Mower decks are becoming weaker and weaker and are designed to be throw-away type products. I shy away from this as well.
3. Durability. Think about it. Most cheaper lawn mowers will mow a perfectly flat "Golf Course" style lawn reasonably well. However, I don't have a flat lawn and I have pot holes and other bumps / ruts in my lawn. As much as I try to fix it, animals (my dog) dig holes, rocks surface, the list goes on. I know my JD 216 has taken 20 years of abuse on this exact property and there is nothing mechanically wrong with it. Granted I've done some maintenance, but it was built to last. The frame is sturdy and the axle stout.
Some of the newer "Garden Tractors" I've seen are scary to me. They use open axles (not sure how to say this, but no axle housings), very flimsy looking front axles and tiny steering componants. Sure they work fine on the flat and level, but I'd bend the frame up in no time.
My whole point of this is that I think too many people don't understand how their machinery works and therefore, don't buy what is practical to their situation. This ends with huge frustruation and usually wasted money. If in doubt, buy as much machine as you can, even if it means going used. Personally, if I had $2,000 to spend on a new machine, I'd look for a used name brand (perhaps a JD 200 / 300 series) with a good old thick deck. Anything less and I'll destroy it. But if you have a 1/2 acre lot that's perfectly flat, many of the lesser machines will serve you just fine.
Just my $0.02...