I think it does make sense to provide a somewhat alternative view and to clarify the matter.
FORTRAN vs. Fortran
First off, one has to distinguish the old FORTRAN from the new Fortran, where, by convention, the name of the old language is written usually in all caps. The old FORTRAN (all the way up to FORTRAN 77) is indeed still used because of tons of legacy code, but the new Fortran (starting from Fortran 90) is used mainly because it is a very elegant and simple yet powerful and efficiently implemented language for number crunching.
DSL vs. GPL in general
Note specifically, that even modern Fortran, in my opinion, is domain-specific language (DSL) and herein lies its relative weakness comparing to some general-purpose languages (GPL) like the mentioned C++: Fortran is specialised for a particular task (number crunching) and might be not so suitable for some related tasks (say, automated analysis of the final results, their graphical representation, etc.)
General-purpose languages, such as C++, give you more flexibility (in language features, in 3rd party libraries, etc.) so that you can solve not just the primary task (number crunching) but also the related task using the same language. If, however, you choose Fortran for number crunching, you often have to use one more language (e.g. Python) for these related tasks. Think about it as of using two different DSLs: one for the primary task, another one for related tasks. Of course, you could also use Python together with C++, but an experienced C++ developer (which you are supposed to be if you choose to do some number crunching in it) would not necessarily take advantage of using another language instead of his C++ beast.
Fortran vs. C++ specifically
All this is somewhat subjective, but anyway, here are my 5 cents. Overall, Fortran is simpler than C++, but (and because) C++ is more feature-rich. Basically, it because Fortran is DSL, while C++ is GPL. And as I said, this is subjective to some degree, and besides, the complexity is one of the most complex things in the universe, so we could start a debate about it, but hey, just one word: templates and the discussion is in principle over. Templates make C++ the beast, but everything comes for its price.
Note that I didn't say that C++ is more powerful, since, in my opinion, "more feature-rich" does not always mean "more powerful". It depends first of all on do you actually need these additional features in the first place or not? Seriously, do you need the level of generosity (and metaprogramming) C++ templates provides for number crunching? Not necessarily. And if so, C++ would not be more powerful than Fortran, although, it will still be more feature-rich.
Templates are not the only feature of C++ that Fortran does not have. Exceptions and Standard Library - are two other noticeable features that Fortran does not have. Again, it is not so likely that you will greatly benefit from these features for number crunching. But some other tasks they might be very helpful, so C++ as GPL includes them while Fortran as DSL for number crunching does not. Think about Fortran as of a "suitcase language" just for number crunching and about C++ as of a "trunk language" for everything.
There is also one great feature of the Fortran language which C++ still could not catch up with: modules. I mean, real modules, and not ancient preprocessor machinery which irritates me more than everything else.