Indeed but it's also a matter of how you design your game. If you're assuming that a game is running off a hard drive, then you'll likely design it so that it loads everything in at load time because the assumption is that storage will be too slow to provide assets on an "as-needed" basis.

On the other hand, if you can rely on there being an SSD you can just assume that you'll be able to grab everything and as when needed.

This actually has an added benefit in that you can design more 'ambitious' games because you don't have to worry about needing to fit all of your assets for a given 'level' into system memory. You can rely on the fact that you can just load and unload things as and when needed.

Not having an SSD is a major bottleneck in performance for any system built in the last 7-10 years already. It's really not an unreasonable requirement.