You do want stereo audio cables connected to your TV in the event that you want to watch TV without the receiver on. If you will always have the receiver on, then johsti is right, you don't need any audio connections to the TV.
You ARE NOT getting 5.1 from your DVD player if you only have stereo RCAs connected. 5.1 REQUIRES a digital connection or multichannel (6 RCAs) analog connection for this. This applies to the cable box too. If it is not digitally connected to the receiver, there is no way to hear 5.1. Now, with TV/CATV, not all broadcasts are dolby digital 5.1; in fact, most are not. So for broadcasts that are not, you will have to use a DSP to "simulate" the surround, which is what you are currently getting with stereo RCAs.