The DVD spec of 720x480 is for NTSC. PAL DVDs are 720x576.
For Blu-ray, 1920x1080 is just one of several resolutions the standards support (however, only 23.976p, 50i and 59.94i are officially supported for frame rates at 1080). Others include 1440x1080 (with a 1.33:1 anamorphic aspect ratio) and 1280x720 (only 23.976p and 59.94p frame rates are supported for 1280x720), in addition to the SD resolutions 720x576 and 720x480.