If only every compiler vendor supported C99 (coughMicrosoft), perhaps C99 would be a usable alternative.

And, inertia isn't the only reason for Fortran remaining popular. Put simply: if you tell a mech.eng./physicist/whatever to write code in Fortran, whatever is produced will likely be fast and relatively readable. Do the same with C/C++, and it will be significantly slower and a horrible mess. Templates-all-the-way-down type of stuff.

Sure, a software engineer could write a C/C++ version that was elegant and as fast/faster than the Fortran code. But scientists don't have the money to hire software engineers. You're lucky if these projects are even under version control.