Are you saying the 787/A380 seats are lighter or the older A330 seats?On the outside they might look the same, but the internals are different with the 787. They have less and different parts to make it lighter.
Noting that the core platform and manufacturer are the same (Thompson Vantage XL) and the seats are in use at multiple airlines, I would've thought the mechanism is common for manufacturing efficiencies and spare parts production.