According to AfterLogic, it's an excessive addition to the list of methods.
The only similar command is:

MyMessage = MyIMAP4.DownloadEnvelopes(Counter, False, EnvelopeParts.Envelope Or EnvelopeParts.MessagePreview, 0).Item(0).MessagePreview

But it has 2 possible exceptions:
1. Item.Count = 0
2. MessagePreview is Nothing

I still think DownloadMessageHeader is not a very excessive addition and will be so easier to use for newbies and the ones who don't want to get in the complex structure of IMAP servers.