I'm looking at copies of the Mass. vital records online. The records are still in the process of being copied & placed online. So, in some cases, I can find the event on an index, but the copy of the record with the details is not attached to it yet (I hope that makes sense).
I can only guess at why the names are spelled differently. Whomever recorded the event may not bothered to get the correct spelling, and just wrote it as he heard it. Whomever reported the event to the town may not have been literate & couldn't spell the name. It's hard to know exactly why, but it was really not uncommon for names to be misspelled on records.
You can order copies of the records "not online yet" for $3 per record from the Mass. Archives. I'll e-mail with details about this.