SINGLE-DENSITY AREA always starts at 0, HIGH-DENSITY AREA always starts at 45150, additional commands aren't needed here. These are to be discussed later for the multisessional discs (though, even they should have REM LEAD-OUT and REM LEAD-IN generating commands, not that LBA thing).
You know that they start there because you are aware of that, but mounting tools do not know it.
Yeah, but anyway: REM NAME / START LBA is also a new implementation that isn't supported yet by any software.
If you want to assign a unique command for dreamcast discs that assumes fixed starting positions, then maybe 'LDA' and 'HDA' are better names.