When you look at a.com, you see it's been reserved since 1993. I think for web.com it's more likely someone just dropped it. Remember back in those days not everyone knew the value of domains .. and more importantly they were quite a bit more expensive ($100 / 2 years I think).
Good question though, you'd expect it to have been taken in the first few years in the late 80's .. 1996 is an eternity later in terms domain age.
I thikn in the early days the system wasn't really about "reserved" names (although at one point that did happen, as is the case with ungrandfathered 1 and 2-letter .com's .. but more that I think your domain needed to be relevant to what you were doing?
Kinda curious about those early days now .. might be worth a trip to wikipedia! lol
ADDED: Seems until 1995, domains were actually free. Which would explain why I thought you needed a relevant name. I think it was the American based National Science Foundation that administered domain applications. I know you couldn't register things like swear words until at least after Network Solutions took over (when the price of a domain went from free to $100 / 2 years). So while it's possible the NSF reserved Web.com .. it's also possible there were no justified registrants ... or .. as I said .. someone simply dropped it. (I'm not sure if you were even allowed to transfer ownership of domains prior to the mid 90's)