Both technologies are clearly very compelling to users.
This is a bit outside of my expertise, but that page mainly points out that DynamoDB supports 3 more language-specific SDKs, while lacking ACID and what appears to be native cross-region replication (through Lambda). Until recently, Datastore was coupled with AppEngine that might explain it.
Datastore and BigTable looks pretty interesting, and I am having a hard time figuring out when to use which (apart from Datastore's ACID support) as both seem a good enough fit for most workloads.
You're correct in that Datastore does provide more general transactions (Bigtable only provides single-row transactions); Datastore also provides indexing and search (Bigtable, like HBase, has a single index: the row key), and Datastore is synchronously replicated cross-zone and cross-region.
I don't think there's an equivalent to Bigtable anywhere. It's so badass it's not even funny - take a look at [0] - a small team of engineers took O(weeks) to build a system that clocks 56 million qps (and these aren't simple bits - 56 million FIX protocol trades and orders).
You can think of Hbase as a clone of Bigtable, if that helps. Bigtable is actually exposed through the Hbase API. /u/mbrukman here is the PM for Bigtable.
Last I checked the pricing was very different; nodes for BigTable, reads/writes for Datastore. BigTable is more cost effective for large workloads, but it requires buying a minimum of three nodes, which is ~$1,500/mo total. If you're small potatoes it seems infeasible. Happy to be corrected if I misread.
This is a bit outside of my expertise, but that page mainly points out that DynamoDB supports 3 more language-specific SDKs, while lacking ACID and what appears to be native cross-region replication (through Lambda). Until recently, Datastore was coupled with AppEngine that might explain it.
Would love to hear more thoughts from you.
(work at Google Cloud)