This idea of one continuous block per level dates back to the PS1 days.

Hard drives are much, much faster than optical media - on the order of 80 seeks per second and 300 MB/s sequential versus, like, 4 seeks per second and 60 MB/s sequential (for DVD-ROM).

You still want to load sequential blocks as much as possible, but you can afford to have a few. (Assuming a traditional engine design, no megatextures etc) you probably want to load each texture from a separate file, but you can certainly afford to load a block of grass textures, a block of snow textures, etc. Also throughput is 1000x higher than a PS1 (300 kB/s) so you can presumably afford to skip parts of your sequential runs.

I meant to write that you probably DON'T want to load each texture from a separate file, but it would be fine to have them in blocks.