Companies that use "leading brand" or "other products" are simply more risk averse (they don't want to get sued). Companies that name their competitor are not afraid of being sued. This could either be because they have proof of their superiority claim, or they are comfortable with the legal risk.

All large companies that advertise have legal counsel (sometimes external, sometimes on staff). Generally, a lawyer will assess the risk of a claim and advise the decision makers in the marketing department of the risk level - high, medium or low. A high risk claim has a higher likelihood of provoking legal action from a competitor, and has to be signed off by a more senior director or VP. However, if they have facts and data to back up the claim, and can defend it in court, they can run with it.

Networks will not allow commercials with superiority claims to air unless the advertiser submits substantiation backing up the claim. Local stations are less strict.

I'm an advertising producer, and I've worked with large advertisers that do the "leading brand" thing. Any time we did a side-by-side efficacy demonstration, I had to sign an affidavit that the demonstration was real, shot and edited without special effects. Companies do sue each other, and have even gone as far as sending a subpoena to view raw camera footage from the commercial shoot.