Altera and Xilinx tools are paid for when you purchase silicon. If your design sells 100 units per year, you aren't going to be paying much. If you are selling a million units, your silicon costs are going to be huge, and a tool that squeezes a few percent more out of the silicon may be justifyable.

Interestingly one of the high end VHDL synthesiser companies admitted that a big problem was companies squeezing performance out of silicon through manual optimisation. For £100,000 they get a lot of engineering effort in a low wage economy.