The handbook currently says that 64-bit Linux emulation is not supported. It was added in 10.3. This is my suggested update to the wording.
There is no rule to avoid markup for the first word in a sentence. The only history of this was due to a buggy shell script that dealt with man pages and has not be used since Linuxdoc times a couple of decades ago.
For clarity, sentences should be written the way they are spoken. The original was better because it did not have that pause in the middle.
I would edit this sentence to avoid the passive wording, though.
<filename>/etc/rc.d/abi</filename> automatically loads the module for 64-bit support on 64-bit machines.
The "64-bit" redundancy could be improved.