I guess it was quite a short article and there are many ifs and buts to what was written.
1) Disk speed - can be divided into a) seek time, b) burst read/write, c) sustain read/write. It all comes down to what sort of work you are doing. a - depends on the hot cache being empty on the drive and is dependent on how long it takes to find the data - and rotation is a function of the spin speed. Burst read/write is from hot cache on the disk and is probably the IO of USB/SATA link limited. Sustain speed will effect larger files and loading large apps - hence the pre-load found in 7/vista. SSD - We have tried Oracle on large SSD - this was poor - worse than standard high performance disks. My laptop SSD is slow too, but I guess this is 3 years old and dying. Careful with Raid 5.0/5.1/10.0/10.1 - make sure you know the difference is - and small files are slower when striped.
2) Vista/7 larger than XP. This was, and still is (see comment above) a problem on smaller memory machines. You should make the distinction between footprint of the OS and the hot-cache preparation; Vista and 7 do have larger foot prints in memory and perform badly on less the 2G; on 4G and more Windows 7 is a very good OS. When computers were small and OS footprints were big in comparison (not long ago), then more memory was the only thing worth upgrading; most new computers come with plenty of memory.
3) Multiple core - well my computers are multi-tasking and it comes down to bang for buck and what are you trying to do (again). For word processing and similar then dual core is good enough, but image processing (photos), autocad and games then you probably need to think about what you want to do. As for hyperthreading (you did not mention this), you get about 15% more speed/virtual cores, but 50% more heat. For laptops this is not good, but for desktops in extreme conditions it might make sense - though I think this more of "mine got more cores than yours".
4) Most problem for people is the slow down over time
a) The large amount of crap-ware provided on a new computer
b) defrag - this should be standard operation - the latest Windows upgrade with something like 32 updates really stalled my computers, and a serious defrag sorted this out. Then there is the debate over partitioning large disks into OS and data and temporary files. For most people this is certainly going too far for the benefit.
c) All the useless applications you accumulate - mostly things you did not know you got from legitamte places.
d) etc....
OK - I have probably bored most people - better go back to work.