My two-cents worth. It's my understanding that some of the big-box John Deere products aren't designed for the same level of owner maintenance as those sold by the John Deere dealer. The ability, and ease of, changing one's own oil should be a given (even if you have a dealer, or local small-engine maintenance activity, perform the service), but other areas might invite questions. My father-in-law's big-box J-D didn't have any grease fittings on the mower deck blade spindles, and it cost him a few bucks extra to have them installed so he could lubricate them each year with a grease gun. My GT235 (from a J-D dealer) has a hydrostatic transmission, and the manual recommends the fluid be changed at each 250 hour point (the mower HAS an hour-meter). And, the transmission is actually set up so I can do the change. It's my belief that those units from the big-box places either have lighter duty transmissions, and may not be designed for owner maintenance (or maintenance by anyone, other than replacement). Also, my GT235 has a 54" mower deck that's fairly quick and easy to drop and pull-out from under the tractor so I can scrape out all the wet grass that stuck to the underside of the deck, and/or change the blades. (I usually keep two sets of blades - one on the tractor, and one that I sharpen up so they're ready to go). So that's my quick summary - the big-box units tend to use life-time (non regreaseable) bearings wherever they can get away with it, you might not be able to change the hydrostatic transmission fluid, and the deck might take longer to drop out and pull out for annual (or more often) maintenance. Just some things to think of.
You're comparing apples and oranges here - the L-series, LA series and the D-series are entry level machines designed by Deere to compete against Sears, AYP, Husqevarna, Poulan, MTD and entry level Cub Cadets. Your GT235 is a garden tractor, also made by Deere but in Wisconsin not Tennessee, and is designed to do more heavier duty chores. One other note, it's not really correct to say big box store JDs when in fact, you can purchase those also at a JD dealer. What we're really looking at here is price points, from entry level to more expensive machines. Your GT235 can't compare to a JD 4x5 series tractors even.