dpi of scans/jpg's: 300 or 72?

hi,
I'm pretty new at this.  I would like your feedback.  I've scan 4x5
transparencies at 300dpi 100%.  Then I resize them in photoshop using the
width and height, but do not change the 300dpi setting.  Finally, I
compress them into jpg's using Fireworks.

I keep hearing folks say "anything more than 72dpi on the web is a waste of
file size". I assumed that meant I could make my files even smaller if I
reduced from 300 to 72dpi. So I did a little experiment.  I started with
the same original 300dpi scan, 1388w x 1080h, file size 4.29mgs.

For the first sample I did what everyone keeps recommending:
1.  reduce from 300dpi to 72dpi using photoshop's "image size".  Doing this
consquently reduced the width to 333 and the height to 259 (file became
255kb).
2.  then I used photoshops jpg compression of setting "6" (file became 37kb).

For the second sample I did not reduce the dpi:
1.  I resized original scan down to 333w x 259h using the width and height
settings  (file became 255kb).
2.  then I used photoshops jpg compression of setting "6" (file became 37kb).

So, the file sizes are the same in the end.  And they look almost
indistinguishable.  Please take a gander at them:
http:/www.mindspring.com/~lmassimo/sample.html

Questions:
Why isn't there a noticable quality difference when I reduced from 300 to
72 dpi?  Weren't pixels "thrown away"?

Thanks!



  

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