Added later: read that blog post. I thought possibly it should come from the irritable snarky gardener?
I think it's a stretch to say useless. To become plant-available, most organic substances containing P have to be mineralized (by bacteria, etc.). It is probably correct to say that mineralization happens faster at low pH. But the bone meal can provide slow-release P over time.
Most plants do not need much P. Probably P as 10 to 20% of the N and K numbers in fertilizers is enough. So, for soil under cultivation that have received fertilizer (the chemical type, or manure, compost, chicken litter, etc.), there is probably surplus P remaining in the soil. The only way to know for sure would be a comprehensive chemical soil test of plant nutrients, but in cultivated soil, a P surplus is more likely than not.