Correct me if I am wrong, MS Sql server isn't true MVCC database and there is some support and it is not default, you have to set READ_COMMITTED_SNAPSHOT ON for the database. They implemented it in 2005. Most microsoft shops don't bother to develop their softwares for this, they are using archaic locking transactions. I've seen many Sql Server deployments keep choking on locking transactions and and people are buyin bigger servers, more Windows and Sql Server licences for each cpu/core to deal with their choked database server.

So while Postgresql's defaults are all about technical concerns, Sql server's defaults are just convenient for Microsoft sales team.