I agree, the more I read about different plug-ins and preamps, etc, and the more I've tried them, the more I see this influence. Of course, some preamps are quite colored and work best on some sources. But many of the modern opamp based models are essentially indistinguishable. Even if you can hear a slight difference in an A/B test, it's so small that you'd not be able to identify it out of context.
The same seems true of a lot of plug-ins. EQs in particular seem to often be just a different interface to the same algorithms, though there are a few that are considerably different (SonEQ is one I use a lot lately, that has a pretty distinctive tone.) The price difference between plugs that sound essentially the same is astounding, too. Valhalla Room is a great sounding, cheap reverb. I'd put it up against some of the $1000 and up reverbs, and I bet no one would no the difference, especially in a mix of a great song.
What drives me a little crazy is reading posts by guys spending big money to get 'the sound' when at the end of the day, the problem is their musicianship/engineering skills. If your song is bad, or the performance is weak, no amount of expensive gear is going to save it. If the song is great, and the performance powerful, the recording is not all that important. As long as the recording meets the basic goal of not getting in the way, you have something that listeners can relate to.
I'd go so far as to say that the whole industry is overly focused on trying to find recipes and formulas for success, it has sort of evolved into something that doesn't look at all like rock'n'roll. I'm rambling, but it seems like we all tend to get into navel-gazing, and it's easy to forget that at the end of the day, we're after an emotional connection between the artist and the listener. Nothing more, nothing less.