if i'm not mistaken, the majority of those organizations still rely heavily on relational datastores, except in the case of exceptional workloads. in addition, i believe facebook has since migrated away from cassandra to the hadoop stack for their messaging platform, though they primarily use mysql (or its successors).
SQL is being replaced in niches that strain its model. elsewhere, it remains steadfast.
I agree, ultimately it comes to everyone's own definition of "tyranny". :) I meant it as "not really having any defensible other choice". (While, of course for example CDB and BerkleyDB have "always" existed.)
I think nobody expects SQL's "market share" to fall to low levels, especially with noSQL requiring much deeper understanding of the data and it's planned use. NoSQL practically operates on a lower layer than SQL does.
Still, it's nice to see people thinking about data storage choices and not going blindly to MySQL/Oracle/etc!
After using MongoDB with Mongoid I strongly disagree with the premise that over the next 5 years SQL databases will be the default and NoSql limited to certain niches. And I know SQL better than most. Alter table ... or db:migrate no more for me.
SQL is being replaced in niches that strain its model. elsewhere, it remains steadfast.