I don't see why they didn't make them open, I really like that feature on my E46. How much more structural rigidity could those small pieces of glass give? It's really the frame around the windows that gives the strength, not so much the glass itself, at least I would think so.
07 E92 335i Saph/Black 6MT
06 E46 M3 CB/Cinn ZCP 6MT - Sold
04 E46 330i Saph/NatBrn ZSP 6MT - Sold