First off, those ads were in the 1990s, not the 1980s (The ad you're probably thinking of came out in 1993 and thus barely makes it under the 20 year rule).

Secondly, you're working under a faulty premise. There's no rule that companies can't mention their rival, they usually don't because they don't want to give their competition publicity or risk libel if they say something provably untrue.

https://www.youtube.com/watch?v=6zyj6xiIOX4

Here's a 2013 Verizon ad that calls out T-Mobile, AT&T, and Sprint by name.