well, by nature, it should be legal under free market economy for one company to make direct or indirect reference to competition's offer (based on facts of truths) in their advertisements in order to create a comparison for the purpose of gaining more market ground.
actually, some commercials done by a cellular provider here in Canada came to me immediately. in the end of each, they always emphasize that their offers are exclusive by saying "...regretably, only from Fido." so without mentioning any names, they manage to create the effect of comparison against all competitions. they've been running that line for a while now, so you get the idea...
