First off: There is a serious flaw in your logic: "Perl, in a way, is just another way for them to advertise their books and services." ... so what, Perl exists just so you'll buy their books about Perl? I doubt that. Perl exists and will continue to exist regardless of wether O'Reilly writes books about it. The fact tha they write books about it can only help make people more aware of perl -- if they make money in the process good for them.
Second: The fact that someone publishes a lot of books on a topic does not mean that "It's obvious they are trying to be a monopoly for Perl" ... The Girl Scouts make a lot of cookies every year -- that doesn't mean they are trying to have a monopoly on the cookie market, it means that cookie market is a good market, and they think they can be competative, so they sell a product in that market. People like it, so they buy lots so the Girl Scouts make more. O'Reilly publishes as many books as they do, because people buy them. More importanly to your specific thesis: a monoply assumes that the company in question is the only one producing/selling an item in demand. O'Reilly is not hte only company selling perl books, and they are not engaged in any practices that I know of to unfairly limit the ability of other companies to compete with them. if you have specific information that contratdicts that, I suggest you take it to the US Department of Justice.
I don't purchase O'Reilly books anymore because I don't like what they're doing and requested our local library a year or two ago to stop their books all together. They said they'd look into it, but since they don't have much money and the IT department is not a top priority, no such books will be ordered any time soon.
That's just sad. I weep for the people of your community, that your narrow minded viewpoint may in some small way prevent them from having access to usefull books, just because you have a (seemingly irrational) predjudice against the publisher.
As for perl.com...
http://perl.org/ is the "community home" of Perl.
- Yes, perl.com is owned by O'Reilly. They bought it, they keep paying the registration, and they use it to provide a lot of good free articles about perl, and the price you pay for reading those articles is seeing their adds for perl books. If you don't like it, offer them enough money that they are willing to sell it, and do whatever you want with it -- but frankly if you have that kind of money to support perl with, I'm guessing a lot of people can think of a lot better ways that money could be used.
If you think it's a travesty that perl.com is owned by a for profit company which promotes the use of Perl, then you have obviously never considered some of the possible alternatives, like http://python.com/