Would you care to speculate what they would cost if they didn't contain advertisements? Would you be prepared to pay it?
Advertising is a fact of life. Neither most magazines nor, particularly, most of the web could exist without it. I've seen reviews which indicate quite clearly that the reviewer disliked the product: there are subtle ways of getting the message across. Carrying advertisements damages nobody's "credibility" (this site included, despite the howls which accompanied the addition of the BH logo).
Jeremy
I never suggested that the mags and web sites should not contain any ads - they could carry ads for things they don't review such as retail stores, photo processors, workshops, etc. Of course that is not realistic and is never going to happen. But, when your existence is dependent on income from the companies whose products you are reviewing, your credibility ALWAYS suffers, period. This is not a condemnation of any individuals, it's just a statement of The Way Things Are.