I'll try to simplify it a bit more so you can understand.
A HDD can't get any faster than what they are now without raising the spin cycle (Velociraptor) but even then a HDD will never have the quickness of an SSD.
Transfer speeds completely aside (the sequential read/write numbers you see) a HDD can only access a file on a platter so fast. Average latency is about 4.16ms on all common 7200RPM drives. An SSD is pretty much instantaneous. Reason being, a HDD has to move the head over to the platter to read a file. After that comes seek time. How long it takes the drive to find the file on the platter. From what I'm to understand this can be different between drives due to the nature of having higher capacity single platters, perpendicular writing, ect ect. It's still the act of finding said file on the platter whereas the SSD knows instantly where it is to access it. The biggest break through between the two is simply no moving parts. We all know how fast RAM is, and an SSD is based loosely on this technology which in the end makes raw transfer speed 5-10x faster than a standard drive.
Most want to compensate in transfer speed with a RAID 0 setup, but RAID doesn't change latency and seek times. In this aspect a HDD will never be as fast as an SSD because they physically can't change those problems. In the end, it's latency and seek time being non-existent in an SSD which makes it so much quicker, and why Windows/general computing is much snappier.
To the cards. Lets turn it around, is it worth the extra for the performance? Yes.