No Gonk you were correct originally. Many of the original CRT based rear based projectors (at least Toshiba's) were based upon a 540p capability and used that to render 1080i. I don't recall the technical details but it was not wobulation which Blogging accurately displayed.

I am guessing it was easier in the early days of HDTV to produce a 540p device then a 720p. It also may be related to PAL and the original Japanese HDTV devices that were all analog.
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