Once they start churning out movies at 1080P resolution YOU WILL notice the difference vs PAL/NTSC or current DVDs and if the price difference is only a small amount (20-30%) most people will pay the extra.
You will only see the difference if you also have an HDTV, *and* if you have it hooked up properly with HDMI. The vast majority of people still have SDTV, and will have absolutely no visual advantage of high-def...
Of course, it's only going to be a matter of time... But barring a complete abandonment of DVD in favor of hi-def, I expect it to take a lot longer for the HD discs to get the market penetration that normal DVD currently enjoys, simply because DVD is 'good enough' for most people.