I liked 8MB buffers because they allow you more leeway to burn without BURNproof on (Less so now, but in the early days, BURNproof did affect the quality of the burn)
These days, the difference between 8MB and 2MB is practically nothing at the high speeds people burn at, so it's not that big a loss as you might think.
The reduction is a decent cost saver, esp. if Plextor were still using the dual-port RAM chips they used to (Allow reading and writing at the same time)
More important is the BURNproof algorithms - These days they are very good so you can rely on them (In fact, at high-speeds you HAVE to rely on them)