That may be what they're doing, but I don't see how it supports the argument for releasing new kits instead of bringing old ones up to date - e.g. Riptide vs revamped Crisis/Fire Warrior kits, Maulerfiend vs Cult Troops and Wraithknight vs every single Eldar special character?
Quite frankly I'd love for our codex to have not a single new unit, but simply to adjust points costs, update rules, shuffle the FoC slightly (through HQ unlocks and Walkers into FA) and resculpt every model over 10 years old.
New kits generate interest for the army outside of the core fanbase that they'd be catering to with only updating the old models. Think of it as newbie bait. Use the shinies to attact them and then BAM you got sales from a whole new target.
And let's be frank, YOU may not care if you get a new unit but I can bet someone else does.