Call it personal experience. When I was in law school (2000-2004) I saw all of these big Inspirons that by year two were shedding parts.
8 out of 10 Inspirons are sheer junk, both today and 10 years ago. I bet some of those you saw back in 2000 - 2004 was the Inspiron 8200, which, as I said in my last post, was garbage. I held on to it for longer than any other laptops I've owned though, just because it was my first laptop and so it had sentimental value. The Inspiron line has an occasion gem, like the 700m that I absolutely adored, but I would never buy an Inspiron that I am not familiar with or haven't done extensive research on, because there's an 80% chance it would disappoint.
In the army they issue us Dell Latitudes (not sure the model, Core i7 so fairly new) and they are built well-enough but are extremely heavy
Unlike the Inspirons, the Latitudes have been mostly pretty good since 2008 or so (except for those plagued by defective Nvidia chips). Yes, some are heavy but some are light. My Latitude E4200 is lighter than any Thinkpad or Apple laptop ever made. I don't like the current Latitudes because they look awful, but that's for another discussion.
Does the E4200 REALLY weigh significantly less than 2.3 lbs of my MacBook Air?
Mine is 2.23 lbs although the lightest configuration (which has a lid without the WWAN attachments that mine has) should be 2.20 lbs. Your MBA is 2.38 lbs and thus 0.15 lbs heavier than mine. Not a huge difference, but noticeable, and it's ironic because your MBA has a smaller screen and a non-removal battery and fewer ports than the E4200. The MBA does feel sturdier and the screen is a tad nicer, but then again my E4200 cost me only $250.
I also happen to like Apple's keyboards, not as much as ThinkPad keyboards, but once used to them they are very fast and comfortable.
The E4200's keyboard is solid and responsive, and is much easier to type on than the X32 Thinkpad that I currently have. In fact, I would say it's right up there with the best Thinkpad keyboards I have used. And it doesn't get shiny like most Thinkpad keyboards either. Except for the low screen resolution of 1280x800, the E4200 is quite likely the best ultraportable business-class laptop ever. If I replace the screen with the 1440x900 panel of the X200s/X201s Thinkpads, I would drop the "quite likely" phrase in a heart beat.