The USA ones have a different amoutn of suction compared to the UK ones. Dyson now measure airwatts at the cleanerhead instead of at the hose suction now hence why the airwattages seem low.
The DC75 actually has similar suction to the DC33- pretty strong suction.
The DC50 has low suction compared to the DC75. One is a small vacuum with limited power, the DC75 is a beast and is actually pretty powerful. The DC75 is 1300W, but should be less than 900W now that the 2017 EU regs have kicked in