I agree. It's a compound noun.

"Product offering" is a compound noun here. It isn't a noun followed by a verb which is what you are trying to make it by changing "offering" to "offered". :)

This is really hard to answer. I'm going to say that in this sense, "offering" is a "term of art". That doesn't mean it has to do with art, it means it's simply a phrase that's used in a particular field or area. I say this because in the field of economics and finance, one tends to see the term "offering" used with financial products. "An initial public offering (IPO) of stock", a "stock offering", a "rights offering" a "corporate offering" etc. Actually, the more I think about it in this context, the more I feel like there *is* a difference: "A differentiation strategy is one in which the product OFFERED is differentiated from the competitors." = the strategy is an on-going, continuous, long-term strategy to make and keep the product different from competitors. "A differentiation strategy is one in which the product OFFERING is differentiated from the competitors." = the focus is on the strategy in the beginning, at the initial launch of the product. The "offering" is that moment when the product is first offered.

Gio, "product offering" is a business, especially marketing, term that means "the collection of products a company offers." You could call it part of the marketing vocabulary. It's (generally) not just one product but many. So here they are saying that the competition between companies is based on having a different "collection" or "product offering". So "product offered" is not what this means. It does mean "products offered", but the accepted marketing term for that is "product offering."

In using -ing, it is refers to an on-going action took place. And for -ed, it is an action that occured at a definite time in the past. ex. The car was cruising along National Highway when it blew up. The car cruised along National Highway yesterday afternoon.