I did find at least one place where http:// URLs are "allowed", and that is in xmlns, BECAUSE, as part of xmlns, they aren't actually a fetchable URL. They are a unique identifier.
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Yes, those are also called concept URL's. Although, to be a good semantic web citizen they should really be reachable to download either the schema or documentation depending on the accept header.
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schema.org and ogp.me were updated to permit HTTPS URLs and use those in the documentation (neither uses xmlns but it's the same kind of identifier). Most of the people working on other standards don't see the point in changing it.