I do think it makes a difference.

Disk performance is not unreliable. I assume that when saying this you are thinking about the unpredictable performance EBS is delivering, but that’s a different solution. I gave you an example of how others are achieving predictable performance with spinning disks (single disk seek per read will give you very reliable and predictable results). And they are not the only ones doing it.

SSDs are needed for DynamoDB (and I’ve covered the reasons in my post), but NoSQL does NOT require solid-state performance.

I see your point, but does it make a difference when we’re talking about running those DBs in the cloud? Amazon isn’t emphasizing SSDs, but I think their use acknowledges their necessity here because the alternatives are memory or unreliable disk performance.

I think the emphasis on SSD is wrong this time. Developers and Amazon do not care about SSD per se (Amazon could care from an economical pov but that’s a different story). I wrote more reasons why I think this is incorrect here: http://nosql.mypopescu.com/post/16076337921/amazons-dynamodb-shows-hardware-as-means-to-an-end