In reply to:
Is there any reason why we're not using 1080i for viewing DVDs?
If by we you mean your family, then the answer is that there's no 1080i content for you to watch.
If by we you mean society, then the answer is that it takes significantly more storage space and current DVD technology doesn't really fit the bill. As such, the DVD forum has been working on several HD DVD technologies though the pertinent companies are in a format battle at the moment.
As to your larger problem, I'd suggest checking a couple other DVDs and if the problem persists, looking into alternative gear because that shouldn't happen. At least I've never seen it.
I forget which DVD player and screen you're running.
