Sine, from what I've read, Blu-Ray's been winning the DVD sales war for a while now but it's not exactly like either's selling like nuts. Although the 360 supports HD-DVD, you have to pay the extra $150 US to get the drive, so it's not exactly the most popular item in the world. That's one thing the PS3 has it beat on, the Blu-Ray is built right into it.
I'll go with Seek on this one in a way. I don't think anyone's gonna care about another format for 5-10 years. People are gonna try to convince you that you should have HD or Blu-Ray for your new HD TV, but it's been a slow-ass process. I don't think my DVDs look too bad on my TV and I have no reason to re-buy my stuff in Blu-Ray or HD; and I'm more of a videophile or nerd than most people.
I think it's mostly 'cause of two things: price and availability. If you got the selection and exclusives people want to pay for, you'll get more interest and sales. And if the price actually comes down so it's barely more than regular DVD, you might see people starting to buy that stuff up, especially if the players come down in price. Even then, I think it's going to be more of a supplement rather than a replacement for regular DVDs.
Before that supplement becomes the norm, it may take 5 or 10 years. Will it be Blu-Ray or HD-DVD that's still around in that time? Who knows...
I was there on that fateful day, were you?