wow, if that is accurate, talk about being a victim of your own success....
Be failed because it existed in the times of Microsoft dominance, Apple didn't buy it, and it had some major technical deficiencies (many of which have been addressed in Haiku).
R5 PE had that partition size because it installed to a 512MB file within your Windows partition, then booted from that file. Personal Edition was meant to give a way to try BeOS without having to have a second drive or do any partitioning. Once booted into it, you could just launch the Installer app and install to any size partition you pleased.
Be was essentially dead decently before R5 was released, so I disagree with the author's conclusion.