They aren't relying on the HPC per-se, but they are trying to grow it.
If they sell 1000 more PC GPUs than they sell in the HPC market, doesn't it make sense to try and change the balance of that?
Lets assume the profit levels are 10x what they are for GPUs, and it is 1000:1.
If they want to increase profits, then which is easier, going from current HPC to 100x HPC levels to almost double profits, or going from current GPU sales to 2x that?
The easiest way to increase profit for NV is to get the high margin HPC market buying their products in much greater numbers. Since the market is probably going to grow at a much greater rate than the desktop market, and the margins are much higher, it makes sense to invest in it while maintaining a high level of product in the desktop market.