Good find shilo! Allen Marriage Index shows both otp.
Having had three wives and as the information on Alfred's death was supplied by someone who probably didn't know any of John's wives, I wouldn't place too much credence on the name Harriet. It's good though that her maiden name was given as Cherry, which seems to confirm the St Albans marriage.
But the problem comes with John who was 14 in 1841. His mother wasn't Ann, but Elizabeth.
I wouldn't get too hung up over names on Australian death certs. The paper trail looks pretty clear; his first wife was Elizabeth Cherry, his second Ann Cherry, his third Harriet Bent.
otp - of this parish
I've seen the 1798 marriage entry in the parish register. Marriage certs didn't start until 1837. There's no other useful information. Both were otp. Both signed with an x. The witnesses were John Garth and William Chaplen.
The St Albans marriage entry can be viewed via the microfilm at your nearest LDS Family History Centre. The only extra information is likely to be the names of the witnesses, and that he was a widower. They possibly married in St Albans as marriage to your dead wife's sister was forbidden at that time, so they didn't want to marry in Luton where they might have been known.
John's marriage cert to Harriet Bent will confirm his father's name, and confirm that he was a widower.
David