Abraham’s response pretty much nailed it, and it appears to be a bug(?) in iWeb. Although I didn’t do anything differently in the design of my name on each page, apparently iWeb DID converted this section of the 2 pages that did appear correctly into image formats – which is why they were ok.
My solution, for those vaguely interested, was to copy my name with Impact font from iWeb into Preview, save it as a pdf file (which kept the alpha channel), and simply re-insert it on the needed pages back in iWeb. Quicker and simpler than Photoshop or Illustrator.
http://www.leskaye.net