Why?! You want to know WHY, too?! 🙂
Below I’m posting a short article which gives a little more information. Basically it has to do with the depth of the scan and the amount of information transferable back to the image editing program. I can’t answer the part of your question about why Elements (and full Photoshop 7.0 for that matter) uses only 8 bit. I’m assuming it has something to do with the complexity of software development in comparison to the perceived return value. But that’s just a guess that has a lot of big words to make it sound knowledgable and important!
The newest version of full Photoshop, CS, can handle up to 48 bit images. I have it, but so far I haven’t had time to sit down and play with my new 3200 Pro scanner and PS CS to see if an untrained eye like mine can even see any difference. I’m betting I can’t but that other people probably could unless the example was pretty extreme.
What you might want to do – as someone else (Chuck?) already suggested – is scan at the higher 16 bit setting and archive an untouched copy of the resulting image file. Someday you might have software that will let you work with that greater bit depth, which I think would be particularly important if you’re working with a lot of black and white photos or negatives.
Here’s part of the short article I found on the web. I’m sure there’s a lot more information available out there, but this one seemed to give a down and dirty overview.
THE EFFECTS OF SCANNING IN 14 BIT MODE VS 8 BIT MODE
The bit depth of an image controls the number of shades that can be defined for a color. The difference between an 8 bit (per channel) image and a 16 bit (per channel) image is not discernable to the human eye if the image is not manipulated but when the levels of an image’s histogram is heavily manipulated, low bit depth images will suffer rounding errors of pixel values resulting in posterization.
Here’s the website address where I got that quote. There’s more there, including a test he ran using a color image.
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http://www.lumika.org/gear_nikon_scan_bit_depth.htm>
