MSRPC allows much more complex constructs such as size_is(len / 2 - 1) and even length_is ((max & ~0x7) + 0x7), a common expression in DCOM IDL files.
For example, the Windows Server domains protocols are entirely MSRPC based, as is Microsoft's DNS administrative tool.
MSRPC is derived from the Distributed Computing Environment 1.2 reference implementation from the Open Software Foundation, but has been copyrighted by Microsoft.
None of the Unix vendors (now represented by the Open Group), wanted to use the complex DCE or such components as DCE/RPC at the time.
Microsoft's Component Object Model is based heavily on MSRPC, adding interfaces and inheritance.