The Lumia 640, 640 XL, 830, 530 and all those other Lumias released are all Nokia designs...Some of them merely have Microsoft's name on them.
To be honest, I am not even sure why people are saying this design is different from Nokia LUmias. It looks like any other Lumia
Nokia certainly did not get every design they did right either...the 920 was derided for its chunky design despite being a fan favorite.
But the 925 was hailed as a great design and what the 920 should have been.
The Lumia 820 was a great design but then you have the forgotten 810 that was incredibly ugly...
So we shouldn't act as if EVERY design Nokia did was perfect and yet they still sold reasonably well(for windows phone) and I imagine these will as well...as far as getting people to switch, well the only complaints I've seen are from Windows phone users ironically.
Even Pro-apple/Android people actually said they don't look half-bad.