A Blu Ray disc will not play on a regular DVD player. Regular DVDs will play on a Blu Ray player.
And with regardes to "only carrying", that is in reference to the Blu Ray vs. HD DVD battle. You will still be able to buy all the regular DVDs you could ever want.
There are only like 435 movies out on Blu Ray, while the DVD Movie catalog is in excess of 60,000. They will not be going away for a long long time.
And on getting a Blu Ray Player, here is an interesting piece from Crave. They strongly suggest the PS3 as your Blu Ray player. Five reasons you shouldn't buy a Blu-ray player yet