Is this true though? Last time I worked on a compiler (admittedly quite a few years ago) Briggs was the bare minimum; our compiler in particular used an improvement over Callahan's hierarchical register allocation (the basic idea of which is that you should prioritize allocation in innermost loops, over a better "global" graph coloring, since spilling once in the inner loop costs way more than spilling several registers in the linear/ setup part of the code).

I would expect that only compilers for immature languages (that don't care about optimization) use naive RA.