For what MPI is good for it's still a good choice. It's just possible that there are no recent books on the topic because the existing ones are good enough and most of us using MPI don't need anything more.
I wouldn't characterise MPI as a distributed programming standard, more a standard for parallel programming on distributed memory computers -- which covers most of the largest computers in the world right now.
If I were betting on it being replaced I'd be looking at Chapel, X10, or, most likely, Fortran 2008.
What you should be looking at depends on your requirements, but if they include high-performance number-crunching for scientific and engineering codes, Fortran or C/C++ with MPI should be in your sights. I've never heard of DataSynapse GridServer, a quick Google suggests to me that it's aimed at a completely different class of computational problems.
EDIT: I just checked Amazon for books 'on MPI'. While the Gropp et al books are a bit old now, there are still plenty of other books being published which cover (use of) MPI. This is, in part, a reflection of the usage of MPI. It's not terribly interesting to computer scientists so there aren't many books on 'MPI for MPI's sake', but it is of interest to many computational scientists, so there's a steady stream of 'physics with MPI' and 'engineering with MPI' books. If these are outside your sphere of interest, MPI probably is too.