Jeez...
Talk about stating the blooming obvious.
Does he also have any wise words of wisdom akin to this regarding thin prov volumes?
Ok for the layman where de-dupe isn't really in use in the consumer field (much), it may be a realisation that isn't pointed out hard enough, but anyone running de-dupe in a commercial environment I would hope already knows this! Then again I don't think at the consumer level you'd be explaining how deduplication, pointers etc really work.
That and his advice only really accounts for de-dupe systems at an object level, if you're dealing with de-dupe at a block level (many tape backup systems?) the ability to release/reclaim space when you have 2Tb+ blocks of tapes even knowing what'll be released when any given volume is deleted will be tricky and will shrink over time when your factoring ratio increases natch.
All IM(own)HO