Why are the HW solutions to “CMOS” posted at CMOSedu?

Yes, you can find (just about) any textbook's solutions on the web, 
most of the time without the author's or publisher's permission.

The solutions are posted to help engineers/students studying the book
and to bypass those that post the solution's without permission.

Note that there are hundreds of "additional problems" posted on 
the book's webpage. Written solutions for these problems are NOT 
available (written up). Most of these "additional problems" ask 
that hand calculations be verified with SPICE simulation results 
so the student knows if they did the problem correctly.

http://cmosedu.com/cmos1/book.htm