From memory, even the Miata Mk.2 has a glass rear-screen.
I too remember that it was easier in the Miata Mk.1 to freeze to death with the scratched plastic rear screen zipped out, than die under the wheels of the 100 ton juggernaut you couldn't quite make out through the haze
Arguably, a tin top with the back seats removed, or a 206CC style "2 crush 2" rear seat would look even more sporty - I know the girlfriend likes the "coupe" styling of the 206CC (the result of a longer trunk/boot to house the folded tin roof) vs. the standard 206.... Not sure if you get this car in the US - Check out the Peugeot UK website to see what they did.
WHY THE BACK SEATS?! Are they expecting family-man to need the 2 rear seats to take the children weekend shopping at the local supermarket?!

It must be some WEIRD marketing manouvre to differentiate it from the Z3/Z4.
Back Seats?....Buy a 3 series ragtop!
Perhaps there's some BMW snobbery going on here, because Mercedes re-introduced the concept of a tin-top convertible
I suppose the one saving grace of the ragtop option is that it does preserve more of the orig. shape and I would guess componentry too, albeit with massive blind spot, plastic rear screen, no heated rear window, less security, less roof-up rigidity, more roof-up road rumble (shall I stop yet?!).
A rag top would pitch the car against the Ford Street-Ka due for launch soon too.