so yeah, not the best analogy.
There totally is. I don't think there's any industry where a customer can really get away with not testing the products of their suppliers. With software you need to test it and confirm you're getting the results you expect, rather than blindly trusting the vendor.
> and any bugs that manifest in said software after purchase treated as the client's fault for not spotting them.
I'm not sure about B2B licenses (I've never been involved in contracts), but I'm pretty sure for a lot of B2C software, the user is responsible for the output and the vendor's liability is severely capped (like no more than refunding the purchase price).
If there is an Excel bug that costs you a lot of money, you the user are responsible. Microsoft's not going to pay you to make you whole (and I'm pretty confident about that, because logically, if it were otherwise the risk to them would be extreme and they'd probably be bankrupt).