This has certainly nothing to do with your pc/OS/router. I run several Linux systems, none of them replied the way yours does. As pointed out already, this is, most likely, a trick played by your ISP.
There are two things that you can do about this. On the one hand, you can study your ISP's behaviour by downloading, installing and running Namebench, a Google test to compare your current ISP's DNS performance against Google's. Besides just timing several possibilites, it also tries to establish whether your ISP performs any kind of filtering, by trying to identify commonly blocked URLs. The report of the test will clarify what your ISP is really up to.
If the outcome of this is not fully satisfactory to you, you may wish to install DNSCrypt, a software package available for several OSes (Windows and MacOS users can find it here) which allows you to encrypt all of your DNS traffic and move it to a seldom-used port. This allows you to bypass ISP's filters which recognize either filter or protocol, and get access to one of a series of providers (chief among them is OpenDNS) willing to provide encrypted DNS resolution. This will restore full capabilities to your pc/LAN, whatever.