Selecting the checkbox to import comments automatically selects the checkbox to import entries: this is because otherwise, if it had been a while since your last entries import, there could potentially be comments that should go on entries that hadn't been imported yet. The data source from LJ that we use for importing does let us just say "yo, are there any new entries since [date of last import]?" and if LJ says "nope, there aren't" we skip straight to the comments stage: it doesn't try to reimport everything from scratch from the beginning.