Well, even assuming that they're using top quality solid state storage, you're going from (at worst) hundreds of nanoseconds per retrieval to (at best) a hundred microseconds per (page) retrieval. Still very significant for some data access patterns.
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I'd guess the most probable reason is to reduce interface stuttering.
Interface stuttering due to swap is an issue on PC's due to hard drive latency, but would it be as much of an issue with solid state storage?
Well, even assuming that they're using top quality solid state storage, you're going from (at worst) hundreds of nanoseconds per retrieval to (at best) a hundred microseconds per (page) retrieval. Still very significant for some data access patterns.