It'll still take a long time if Blu-Ray becomes standard for BD to overtake DVD's. When DVD's became popular people did not have the collection of movies and TV shows on VHS like they do now on DVD. Thus there wasn't the major financial hassle of repurchasing the movies on DVD. I doubt today people are willing to repurchase alot of what they have on DVD. The DVD movies and players are so much cheaper than what VHS ever achieved in its time that people probably have one for each TV, possibly a portable DVD player, DVD player in each computer and a DVD player in their car. These are hurdles HD has to overcome to become mainstream not to mention getting more HDTV's into homes. Until then it's still a niche product.
Edit: BTW I own both a Toshiba HD-DVD($99 FS BD
) player and a PS3. So I'm not some DVD fanboi.