I wonder whether there's been some kind of legal/copyright reason for the wave of logo changes in the relatively-recent past. Remember that Marvel (slightly) changed theirs, as seen on the more recent Omniboo

The problem at Marvel, for years (more than a decade?) they weren't using their own logo on their book spines. They were using type that was relatively close, but the fact that it wasn't their actual copyright logo, meant they were "diluting their own brand" and not enforcing their own trademark. That's a big no-no and could force them to lose their brand, or unable to file suit against others properly when/if necessary.

DC's previous logo was too close to DC Shoes, and was never properly trademarked their logo.
they were having to pay a fee to DC Shoes, so they eventually came up with something new.
http://www.comicbookresources.com/?page=article&id=19263

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