Objectivity - is a significant principle of journalistic professionalism. Journalistic objectivity can refer to fairness, disinterestedness, factuality, and nonpartisanship, but most often encompasses all of these qualities. wikiP
That, in a nutshell, explains why TAS, Stereophile, and other print and electronic publications of similar type shouldn't be regarded as journalism. Their readers would be well advised to view them as entertainment only and to take everything they read there with a grain of salt.
As a practical matter, you can only gather information on what gear to buy from four sources: your ears, your friends, the magazines, and the internet.
Your ears are limited by time, experience, and access. In my case, very limited. Your friends' ears have those same limitations, and the added ones of their objectivity and perceptiveness. The magazines are not limited by experience or access, and because they have to stick their opinions out for public review monthly, their ability to remain wrong (or biased) is inherently limited. On the internet, anyone who can manage to fire up a blog can pontificate as if they had actual experience.
Ever wonder why so many people talk about the AK community, and love AK Fest? One reason is because the community aspect of AK causes people to "publish" on a regular basis and be subject to criticism. Once you make friends on AK, and meet people at the Fest, and wander round the show comparing likes and dislikes, you get to experience a wide range of gear and the range of reactions to the sound. Eventually, you get a good sense of which opinions are helpful to you, and you learn from those... almost like a professional reviewer!
Are the magazines influenced by advertising? Sure. But, as above, that influence is sharply limited by other advertisers, each of whom wants a favorable review, and by public reaction. They can only be wrong for a short time before losing readers, and when you lose readers, you lose ad revenue. The point that all their advertisers are in audio actually cuts the other way. If they lean too heavily in favor of one mfr, others will cut their advertising. In a more general publication, that effect isn't as profound. You can conclude they're not "journalists" and refuse to read them if you want, but that leaves you with sources of information that are either very limited or completely unreliable. I like the magazines, and I think we need more of them.