All the PC's suggested are substantially larger (15.6" vs 11"), and thus may be less appropriate for the OP's situation, for example if you walk long distances to and from college. Barring Atom-powered netbooks (which might actually be worth considering), similarly sized and specced PC's end up in a similar price range. Keep in mind that the small form factor of the Air/similar-laptops is a plus for the people looking at these sorts of computers. The graphics cards are useless deadweight unless you actually intend to use it for gaming, which depends on the OP.
The Toshiba has abysmal battery life ("Up to 3 hours, 4 minutes"), and the slow mechanical hard drive will be more of a detriment to non-gaming activities than the integrated graphics would be. The dedicated graphics appear to be about 50% faster than the integrated graphics on the Air, a bit helpful for gaming I suppose but hardly a game changer.
The Asus gaming laptop is better, up to 5 hours, but the Air nearly doubles that. If your not indending to game on it, then the extra CPU/GPU does nothing other than add weight, size and lower battery time. Still uses a slow and clunky HDD. If you were intending to game regularly, it looks pretty solid. But if you already have a PC to game with, or are just not interested in gaming, then it's only slightly cheaper than the Air.
The refurb dell you linked to has an ancient Sandy Bridge processor (4 year old architecture). The processor would probably not be that much faster than the much newer one in the Air, and the integrated graphics in the Air is considerably faster, which would ironically make the Air the more capable gaming laptop here. The older processor is also rated at 3 times the power consumption (45 vs 15 watts). Battery life is not specified, nor any statistics, but would probably be pretty poor. As a refurb, I would be concerned about battery wear further reducing battery life. It is cheap though.
The laptops you mentioned are a somewhat more performance bang for your buck, but with significant compromises in other aspects, particularly portability, which is traditionally one of the more important aspects to consider when buying a laptop. It depends on what you want to do with it though.
If you are going to college, you may be eligable for a student discount. here in Australis it's ~10%, so that takes the price of the Air from 900$ to 810$.
Since word processing doesn't exactly require bleeding-edge technology, those specs on the Air will last you as long as the computer survives, technical-obsolescence be damned. Given their construction, that will probably be as long as the battery lasts (They are built like tanks). Given that the battery is literally glued to the case, it's worth factoring battery life (as in how many years before it wears) into your decision too.
If you don't intend on downloading masses of things, 128 gb SSD will be plenty of space, and also be MUCH faster than a HDD. That depends on your use case though, if you prefer to have tons of storage, then the HDD would probably be better.
Laptop touchscreens are a gimmic IMO. They really should be left to the tablets and All-In-Ones. The trackpad on the Apple laptops are effectively the benchmark standard for good reason, they are of excellent quality. PC trackpads are a bit of a crapshoot, being anything between "Apple-like", and "piece of shit". They have improved substantially though.
In the end though, if all you want to do is type reports, and you don't need an all-day battery of particularly small form factor, than a cheapo $300 plastic PC laptop will do wonders and save you a fair bit of money. Ontop of that, as long as you don't actually treat it like a $300 cheapo laptop and
actually take care of it, it should last you years. If you want to game, you can put the $500 towards a PC box, because PC graphics card will curb-stomp laptop graphics card for the price.
A netbook may also be worth considering, however the Atom processor will effectively limit you to exclusively word processing and light web browsing, and the screens are usually of very poor quality.
Both Windows and OSX work fine as operating systems. The only problem is that some Windows resellers load their computers with tonns of shit that nobody wants and that makes them perform worse.
Future moddability. Laptops are pretty much built in one piece, and mac has done enough that their laptops are just as changeable after purchase as most windows ones are (i.e., swap out ram and the hard drive).
This is incorrect for all models except the non-retina 13 inch model. All other mac laptops are held together by torx screws, have ram chips soldered to the main board, batteries that are literally glued to the case etc. You might be able to swap out the SSD, but thats about it.
Dismantling these things is no easy task