A fusion drive IS an SSD plus a normal HD as well.
e.g. the Fusion Drive in my Dad's iMac is an 128Gig SSD and a 1TB spinning HD.
They just called the combination of both drives, plus their dynamic allocation software a "Fusion Drive".
Put your apps and OS on the SSD part.
So no, a pure SSD is not much faster at all.
They want the mbp's 512Gig SSD as well as £400 in exchange for a 1TB SSD, which is crap.
The SSD+HD option (Fusion Drive) is cheap enough to be available in all mbp configs fitted as standard, but they chose to make it thinner, lol.
As for the last comment about how much money I make, that's not the point. If you want to get screwed over by Apple then bend over, but don't expect me to take it too.
Erm...SSDs are faster than fusion drives. The algorithms used to allocate files to the SSD part over the HDD part are not optimal. In addition access files on the HDD would have increased latency, such as opening large files. Don't try to deny the laws of physics, you weakens your argument.
A fusion drive would also increase the size of the MBP which would be a step back.
The last point is the point you should take to heart. Apple rMBP is a premium product, they are usually ahead of the curve (such as getting rid of optical drives) and if you don't want to pay above the price of the hardware, don't buy apple, buy another product.