The convention used in the Unix manuals, such as the cron man page from V7, is to capitalize the first letter of utility names when used at the beginning of a sentence, and to use their normal (almost always all-lowercase) spelling within sentences or when they're used in examples.
This convention is used even when the utility name is an acronym, such as dc - desk calculator.
User @Nobody pointed out in the comments that Debian's man pages always use the all-lowercase spelling, including at the beginning of a sentence. This appears to be an editorial decision; looking at the patch file in the Debian source for cron, patches are made to the original Vixie Cron man page, to change
.I Cron to
.I cron. This is also the case on Debian derivatives such as Ubuntu.