of course there will always be a few people who buy them, but most people going to buy a new macbook now arent going for the white one because it's now outdated. its like this, in a few years the aluminum will still be here and the white one won't. so you may as well get the newer computer that's a bit more futureproof if you're already in the process of getting a new computer. also in this case, the new ones are superior
see this is speculation.. you dont know for sure, there might be a high probability, but that is not the same as knowing what apple is going to do in the future. if they are having increased polycarbon macbook sales, they wont discontinue it. that's apple being rational.
also, what is this nonsense about being future proof.. as of now polycarbon macbooks have the same c2d cpu, and 9400m video card, both have nvidia chipests (granted the polycarbon doesnt support ddr3, but theres no real performance advantage yet. ddr2-800 will perform as well as ddr3-1066), chicklet keyboard, lets see thats all i can think of off the top of my head, but the main thing you get with the unibody macbook are... led lcd, multitouch pad, maybe a better webcam, and better battery. these are just commodity enhancements not really affecting the "futureproffness" of the white macbook.
http://www.macworld.com/article/136214/2008/10/macbookbenchmarks.html
if you look at the chart the last white macbook 2.1ghz with the intel chipset was pretty much neck and neck with the unibody 2ghz macbook. with the updated insides and having the same gpu, the white should outperform the unibody (i havnt taken in account of the .1ghz difference though from the intel chipset vs nvidia chipset white macbook), the things that the white macbook does worse than the unibody macbook are suites, and frame rates, which should be a lot better with the new chipset and gpu.
before you start talking out of your ass do some research... its kinda annoying hearing fan boy rabble.
notes:
http://www.breakitdownblog.com/ddr2-800-vs-ddr3-1333-does-speed-matter/
http://www.anandtech.com/memory/showdoc.aspx?i=2989&p=1
side note:
also, if it wasnt so economical for me to buy a macbook, i would buy a thinkpad x200s (maybe x200, but id rather have the led backlighting). the price of my configuration of a x200s is $1700 ($1350 for a x200) vs the macbook at $949 w/ student discount (my real price for the polycarbon macbook is only $459, correspondingly $749 for the unibody), weighing it out the led lcd, and multi touch (these are the main things i want though) are not worth the 250 extra bones. I WANT IT, but I cant justify the extra cost. If only I could make my cake and eat it too... multi touch led lcd polycarbon macbook.. oh sweet jesus.