Why not just include a real BOM!
Well, for instance, freeduino was designed without specific parts in mind, and the prototypes were built largely with "surplus" components of unknown part numbers and usually unknown manufacturer (and not always matching the schematic. I have a partial reel of 9.19k resistors that were used in place of the 10k reset pullup on the 1206 version, and a big bag of .22uF and .33uF ceramic caps that I used instead of .1uF bypass caps. You're lucky the schematic values aren't "bypass cap" and "pullup resistor" (Hmm. I think I actually did "LED current limiting resistor" rather than specifying an actual value.))
It's a FEATURE of a hobbyist open source design that the parts used are generic and widely substitutable, but it makes it really annoying (for the developer as well as the would-be builder) to track down REAL part numbers. (I suppose I could look up part numbers in a catalog, but if I'm going to go to that level of detail, it would probably be nice to actually TEST those actual parts, right?) (What? Spend REAL money?)
That said, I do like the Adafruit projects whose parts lists point to actual mouser/digikey parts OR specifically specify "generic." And a surprising number of parts DO have specific limitations that ought to be mentioned somewhere (like the power supply electrolytics on a TH freeduino should be "short" (5mm, 7mm), or the shields won't fit right.)
I'm not really very fond of BOMs that have meaningless manufacturer part numbers instead of calling out the important features of the part (very common in manufacturer "reference designs.")
I suppose that somewhere there is a happy medium.
(Meanwhile, if you build something based on an OSHW design, using all new parts with known part numbers, it probably IS a good thing to contribute back to the community. Also negative result info: "don't use a 1/8W resistor here, because it's actually dissipating more than 1/8W!") FIghtCube's example is great. (well, almost great; it looks like the links don't work (digikey's fault for tying "search" to a session?)) I do notice that it apparently took several months to put together!)