1. First off, anything "can" do well if maintained well. A well-maintained $800 Murray can last 5x as long as $5000 Cub Cadet that isn't.
2. Most brands use the same engines. Hence why you see Kohler, Briggs&Stratton, etc, in darn near every brand. They are often the same base engines. However, there are differences. John Deere for example will replace a few of the engine parts to make them more durable. It's not a ton of difference, but it could be. I'm sure many more of the upper crust brands do this.
3. What are your needs? An $5000 Scaggs could last you a decade easily, but if you only have an acre then it could be massive overkill. However, that same Scaggs machine could cut that acre in half the time of the average $1500 mower.
What is your yard like? Is it nice grass or is it a converted hay field? Hills? Rough or smooth?
4. Quality vs Quantity. You could but one $3000 Cub Cadet that will last you 10 yrs. Or you could purchase a $1500 Murray that will last you 5.......then, just buy another.
5. Deck. If you have a nice, smaller grass yd without a lot of tree roots, landscaping, etc, then your average deck will do. But a stronger fabricated deck may be the way to go for tougher yds.
6. Shop around. In Richmond, I priced a 22 HP (B&S) John Deere ZT with a 48" deck for $2999 at Lowes. Then went to Bishop's downtown (local place)......who had a 25 HP (Kawasaki) Cub Cadet ZT with 54" fabricated deck for $3099. And I could trade in my old mower at Bishops for a price. Not all prices were like this. Bishops had a few that were more expensive than Lowes.......kinda just relied on your needs and what you were looking for.
7. In general, name brands are a little better. For example the average John Deere is going to be better than the average Murray.......but it's not like it's a huge difference. Also, in general you get what you pay for.
8. I've heard that most residential mowers are designed to last about 200-300 hrs of use.....if maintained properly. More commercial mowers can last double this.
A quick Google search found a Consumer Reports detailing this to be true.
http://www.consumerreports.org/cro/...-a-used-lawn-tractor-at-a-yard-sale/index.htm