In articles/forums about PC gaming I always see people saying how Solid State Drives only make games load faster at startup (of the application) than they would with a Hard Disk Drive, and that an SSD doesn't improve the speed/performance of an application that is executing (after startup) in comparison to a HDD. Now I imagine that the first part of this is because during application startup, the operating system needs to fetch all of the application's instructions from the disk, and load them into RAM. And since SSD access is a lot faster than HDD access, program startup with a SSD should be a lot faster than a HDD.
Now what I don't understand is how this doesn't also affect programs that are currently running, since the OS can move a running application's memory pages from RAM to the page file/swap space on the disk. When the running program needs to access a page that was moved to the page file/swap space, a disk read needs to occur in order for the page to be brought back into RAM to be used by the application. So wouldn't an SSD also provide a performance increase here too, as opposed to just in application startup?