"Web scale" isn't a real thing and I don't know what "shared data access layer" refers to but relational databases have decades of features and tooling that prove to be very useful in most cases. Even if you don't use ACID, transactions, key relations and other features, maintaining the basic type information in the database still has numerous advantages in data consistency, integrity and performance.
Also everything can scale, and it's all using the same fundamental primitives (sharding, etc) to do so anyway. Some just make it easier with built-in functionality vs external layers.
This is not to say that non-relational systems aren't useful, but that they are rarely used correctly instead of chosen for marketing hype, and hearing things like "adding a column is easier" from an architect usually points to the later situation.
Also everything can scale, and it's all using the same fundamental primitives (sharding, etc) to do so anyway. Some just make it easier with built-in functionality vs external layers.
This is not to say that non-relational systems aren't useful, but that they are rarely used correctly instead of chosen for marketing hype, and hearing things like "adding a column is easier" from an architect usually points to the later situation.