People also aren't accurately answering the question.
If you have a 'widescreen' DVD, then the odds are that it has been encoded as an anamorphic image which is using the full 720x480 resolution of the DVD that is avaialble to it. For 480i CRT SDTVs, you do have a loss of image resolution and quality when you drop from the full 720x480(i) to the more common 640x480 (SDTV), and with 2.35:1 films you drop further to 640x272 which is, overall, about a 50% reduction in the total number of pixels which could be delivered by the DVD.
Yet, unless you are sitting right on top of the TV you may not see this loss of quality. Likewise, CRT displays are much more forgiving when it comes to lower quality sources than digital displays such as plasma, lcd, lcos, and dlp are.
I have many diatribes about this, but it is far more important to have good color and image processing, such as that which CRT can deliver (great black levels!), than getting more resolution. But, getting both is a big plus.