I don't have the low down on Windows 7 RAM caching, but I would venture to say that its not as effective as you're making it out to be. ...if you continually open the same program over and over all day long, the benefits of a SSD may be diminished (not eliminated). But if you're like most people where you open/use 2 or more programs in a particular "session" then the benefits of an SSD far outweigh RAM caching.
Windows 7 turns off caching if it detects an SSD for the exact reason you're concerned about.
I usually tweak Prefetch and Superfetch to only cache the boot files for mechanical hard drives. The cache just seems to get in the way for applications, and after a while of accumulating cruft, it slows down boot times. It would be better if the user had more control over what they cached.
I think a sort of quasi-placebo effect might revolve around people putting clean installs on SSDs (rather than mirror some existing install or whatever from some old mechanical drive with millions of programs, etc).
Has TR benchmarked Firefox vs Firefox loading time/memory use with same addons used normally/ on Ubuntu vs Windows 7, and grouped by mechanical drive vs SSD? That would be fascinating to me.
I'd be stunned if after the computer booted up and one of any of the relevant applications was loaded up that it'd really be bogged down some sort of significant, since it would obviously be accelerated by RAM and preloaded given ubiquitous cheap RAM versus long-term storage.
I've gotten to play with brand new Win7 SSD laptops and mechanical laptops side by side (these were brand Dell 6520 laptops for work), and the lag from the mechanical disk is noticeable. A clean install of Windows always helps things, but the lack of latency and the bandwidth available is something no caching program can over come.
The Firefox comparison would be really hard to do. Windows and Linux handle memory and virtual memory very differently.
Yeah, as long as stuff doesn't start to swap out of RAM the times would be very similar. Once things start to swap out, the SSD would have an advantage.