You need to think of the phrase "all licensed amateurs" as meaning "all appropriately licensed amateurs" and it all makes sense.
You quoted the wrong person. It's the OP who needs to define their meaning of "All" amateurs because as indicated elsewhere, Technicians in the US CANNOT
get on 10 Meter FM (We can however get on 10M SSB from 28.3 to 28.5 & (If we want to) CW from 28.1 to 28.3)
Cheers & 73
If the Tech is transmitting above 51.0MHz on FM and is crossbanded by a rptr on that band to 10m, it IS legal....but no, a Tech cannot transmit direct on 29MHz FM...