I think noise in the A900 is a non issue below 800, printing or when viewing on a monitor. The problem with Sony A900 cameras, as I understand it, is the increase in noise at 1600 and above. It's not that it is particularly bad, it's just that it compares less favourably with Canon and possibly Nikon. Nikon uses the same sensor but their in camera software is different. That could be corrected by Sony with a new firmware revision, as they did with the A700.
However increased noise will not be improved if you shoot RAW and if you shoot jpg and your theory is correct, then when printing with jpgs taken at 1600 ISO or above, new firmware revision or not, noise will not be an issue.
Many say that removing noise, in RAW or jpgs, is best done during post processing using noise ninja, neat image or Adobe ACR/Photoshop.
I certainly do not think the noise in an A900 is there for a reason, nor would I call it a flaw. It is more a balance of how much does Sony spend to produce a class leading camera with huge pixel count and very high dynamic range and keep the price below $3000. Looked at that way, then putting up with slightly more noise above 1600 is a no brainer. JMHO.