Currently Being ModeratedDec 7, 2012 6:51 PM (in response to heddoimvee)
You Mac doesn't care.
Most likely your DNS server is doing this to you.
You generally get your DNS server from your ISP.
You can specify a different DNS server is you want.
System Preferences -> Network -> Advanced -> DNS -> DNS Servers -> [+]
Sometimes it is possible to configure your preferred DNS server into your home router, but since every router has different configuration instructions I will not try to specify how to do that.
Currently Being ModeratedDec 8, 2012 8:25 AM (in response to heddoimvee)
You're connected on a private and particularly an access-controlled and restricted network, and the administrators of that network have decided that connected users shall not expend available resources and bandwidth with access to various web sites and/or web services.
If the network administrators have established the blocks correctly, you'll need to use fairly advanced techniques to bypass the blocks, and attempts to bypass these blocks — whether the bypasses are successful or not — may well be considered grounds for network disconnection and/or disciplinary action by the organization.
It's common to log these sorts of failures and attempts to bypass, and — given they have control of the switching gear — it can be feasible to uniquely identify the client computer that's making these requests. If not the specific identity of the client computer system or the credentials used, then the location of the client computer that's attempting the connections.
Check with your network administrators, and with the site's policies and procedures.