I'll speak for me.
I have never been asked to do so, either -- and, like you, I don't pay attention to who advertises with TR, though right now I see an IBM ad, and I vaguely recall having seen some Microsoft ads. Anyone who thinks I'm taking money to give Microsoft positive reviews hasn't been reading very closely, anyway.
In about half a dozen years of writing literally hundreds of articles for TechRepublic (edit: averaging something like one every 4.5 days -- more often toward the end, less often toward the beginning), my experience with regard to reviews and expressing my own views has not varied one whit from what you describe. The few times I have been asked to alter the content and views in my articles, there have been zero correlations with any vendors, products, or service providers that I discerned.
