I'd completely forgotten about that - that's right. It's been ages since I've watched those eps so I don't even have a theory as to why he did them rather than one of the actors in each ep who wasn't in the teaser, which was the normal practice. It can't be that all the actors in those eps were in the teaser, can it?
And I'm sure many noticed this a long time ago, but it wasn't until I just went to check the Episode Guide that's printed in the DS Memories book that I realized that, unlike the separate Program Guide, among other things, it doesn't even list who did the opening voiceovers for each ep. How strange...