What percentage of Higher Education Institutions use Drupal?

There are a lot of issues with overviews like that. To start with many non-American universities might have a .edu domain just for the university homepage and country specific domains for the majority of their sites. At the university I work the pages on .edu are static landing pages (i.e. no CMS). However, the rest of the thousands of sites are run on almost all CMS available with Drupal and Wordpress being the most common, but including Joomla, Sharepoint, Typo3, Sitecore and custom applications as well, but all of these would not be counted in the first source. Our university would just appear under no CMS.

Furthermore, it raises the question what classifies as a site and if all sites are equally important? One unit runs a Wordpress multi-site install for course pages. These are very simple sites basically with commenting and post submissions. Should these hundreds of sites be counted the same way as a single site by a major faculty with much more complex functional requirements, e.g. integrations into other systems etc.? Quantity has become a rather useless measure when technology these days allows everyone to publish an unlimited amount of sites in a matter of hours.

Any CMS these days can do the basics of publishing content, providing themes etc. Which one gets picked is often simply the result of familiarity and preference of a decision-maker.

The really interesting insights could be gathered through questions such as why a university picked a specific CMS for a specific use-case (neglecting biases such as mentioned above, e.g. familiarity, budget, availability), objective evaluation if a particular CMS is better suited for some use cases than others given the way it is designed, availability of modules/plugins etc.

The second survey at least looks at some functional requirements, but these tend to be on such a high level (e.g. workflow) that they are useless...

I just got done with a manual review of every college I could find within a 50 mile radius of the one I work for. (Did it this way to make it harder to game the results.) Mostly I used the BuiltWith profiler widget for Chrome, but I also peeked at the code where that couldn't identify the CMS.

It's a mess. Mostly noise. about 25 schools, and the greatest number using the same CMS their main website is 3, using Drupal. (I haven't tried hard to dig into the subsites yet. It's going to be hard to figure out where it still matters.)

The greatest number by far use "unidentified" (as I have so helpfully described it in my spreadsheet).

About 3 institutions (soon to be 4 when I bring a new subsite online) use Drupal for at least parts of their main site. 2 (soon to be 3) of those use some kind of a sub-site strategy. (That's if I don't count the Cornell extension that has an office about 15 miles from here, in downtown Rochester. Most of Cornell's school/college/office sites are Drupal, while the marketing-focused 'www.cornell.edu' pages appear to be something else -- I figured it out IIRC but don't remember.)

1 fairly large school (University of Rochester -- you've never heard of them, but they're institutionally massive) uses Wordpress for their very large main site. I'm not even sure how one does that; I haven't looked in detail, but I think I would probably find they don't do a lot of data integration with their systems of record.

So what I'm seeing is that for schools with a lot of resources, it's common to have a front page area that's either bespoke or fielded using some kind of marketing-focused CMS, while the child pages are built using something else.

There are a number of CMS in use in our region that BuiltWith simply doesn't track -- whether it's because their usage is low or they're just plain hard to track. (In my quick survey, I seem the failing to track Umbraco, Fission, and Blackboard*. All 3 should be easy to identify.)

EDIT: They do track Umbraco & Blackboard, but don't seem to be able to identify them on the sites I looked at. Which is another argument for taking automated profiler-driven surveys with a grain of salt...that said, all the Drupal sites I've looked at with BuiltWith were correctly identified.

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*Yes, people actually try to do this, though it's mostly as an intranet. I try not to judge. It's usually that they can't afford the time to learn something else, and I know how that is.