A recent study by a professor at Ithaca College found that very few libraries include RPG books and resources with in their collections.
Based on review of the Online Computer Library Center, a database of 72,000 libraries, very few libraries have even a single copy of an RPG book in circulation, in spite of the genre's 40+ year run.
Interestingly, there may be some data gaps, as the search was by ISBN numbers, which weren't assigned to early additions of TSR manuals, or their contemporary Runequest books.
The authors posit that inclusion of the manuals in the reference stacks have value for library -sponsored community gaming events (40% of liraries reportedly host gmae events of some type), as references for academic or similar study, such as their influence on the video gaming industry and game theory.
Anyway, an interesting read.
Link to download report