I actually preferred the use of a cartridge in Blu-Ray. Anyone that has Netflix can tell you that DVD's are way too fragile for anything but the most careful handling and care. They scratch too easily.
I understand that Blu-Ray will use some sort of "hard coating" on the discs to elimiinate the need for a cartridge, but I strongly believe that they won't be as durable as media inside a hard plastic case, like minidiscs. THOSE are some durable discs!