Wrong. HD speed improvements have been pretty flat, and has been far outpaced by HD capacity which is closer to Moore's Law. SSD offers a nice boost in speed. Don't just throw around Moore's Law as if you know something.
Say you have an SSD that consists of 8x16GB chips. Internally it's implemented in something like a RAID0 array, which is why they're so fast. If the capacity doubles / size shrinks by a factor of 2 and someone decides to stick 16x16GB chips in the next gen SSD then you will see a speed increase. On the other hand if they go for 8x32GB you won't.
My comment was directed to Matt_Cutts' complaint that he didn't know when to buy an SSD. I don't think it matters exactly when you buy one. (Though I personally am waiting to see how Intel's 25nm SSDs compare to those based on the SandForce SF-2000 controller around Jan/Feb 2011. Maybe I should practice what I preach.)