UPC and SKU
SKUs are company specific. UPCs are unique. 12 digits = 1 billion. Sounds like too few to keep up with the bunch of products that exist today.
For the case of the Open Source Economy, where Distributed Market Substitution becomes a reality based on optimal products - the case for the UPC becomes strong. Keeping track of best versions is a good idea. Identifying an optimal version can promote its replication. Identify building block Modules in a Construction Set Approach can lead to collaboration. From the standpoint of generative construction sets - identifying the critical building blocks is important. Here OSE can join with UPC and GTIN standards to facilitate the open source economy.
Note that in the immediate sense - SKUs should be built upon the UPC - for transparent operation of Distributive Enterprises. Note in the article above you cannot price match on SKUs - these are company-specific - while you can on UPCs. It appears that an Optimal Economy would involve the transparency of the UPC.
UPC and EAN
UPC is north America only - rest of the world uses a 13 number EAN 
Standards, such as the UPC - facilitate identification. Thus - find the UPC to get unambiguous specifications.
For example - Menards says B816RR is 6 lb load rated - but searching under the UPC shows it's actually 50 lb rating. Trust the rating on sites that appear to have comprehensive information. To find a UPC - you can typically search for a Model Number (B816RR) and find a website that also shows a UPC for that product. In fact - sites with the UPC listed are naturally more transparent and trustworthy - as they allow for product cross-referencing - with any site that uses the UPC. Specifications should be thus reconciled, and identified with a good level of certainty.
TO be reconciled: