1script - 3:10 pm on Aug 6, 2012 (gmt 0)
Back in 2006 I had a site banned from Google for 2 years for just that - making site search pages index-able and then a page with a list of the most popular keywords was linking directly to the site search pages. These then become the classic doorway pages that Google does not like. In fact, Matt Cutts had specifically spoken out against having those search pages indexable. Unfortunately for me, it was after my site was already banned.
Fast forward to 2012. I am habitually adding instructions to robots.txt to disallow search queries. However, most of my competitors (*how sites and clones) are ranking (and outranking me) with what looks like either a search result page or an empty content page that only has the keyword in the title and H1 and looks like they either plan on filling it out with content later or just simply creating hundreds of thousands of doorway pages that way. Sometimes you can see a page that says "No results available" and it still ranks!
And, yes, it was a very astute observation: all these sites have a custom AdSense code, not the regular one. I think I even have a "less sinister" explanation for why they are getting a pass. It looks to me that since the custom AdSense is less clearly marked as an ad and they have more leeway in styling it similar to the rest of the site, fewer people complain to Google and report those pages as spam.
It's either that or their AdSense account reps do indeed meddle on their behalf. And they don't even need to do much. They don't really need to alter any algos to make the doorway pages rank. All they need to do is to call the spam team and say:"these guys are OK". Most of what they rank for is very long tail and does not take much to rank for. This way everybody gets to keep their face and say that being a premium AdSense publisher does not affect your rankings. It's true, it doesn't. It just affects whether you'll be wiped off the face of Google for the serious infraction or not.
And, by the way, what a novel concept: an employee of a large corporation picks up her phone and dials a 5-digit extension of another employee or meets her at the water cooler. Millions of dollars of revenue can be affected by one little chat like that and it does not even qualify for insider trading, so can be done with complete impunity. Are we all so naive that we should believe this *never* happens?