grammaticality - Relative adverbs: when vs where

Source: p 39, The Law of Contract, 5 ed (2012), by O’Sullivan and Hilliard

2.83. ... We have seen that the general rule is that displaying goods in shops only constitutes an invitation to treat, although there are good reasons for taking a diff erent approach (paras 2.22–2.23). However, what of a typical website that allows the customer to select the item, enter his payment details and seemingly conclude the agreement online. In this situation, then (absent the terms and conditions of the site providing to the contrary) it is suggested that it is clear that a contract has been concluded ... The natural inference is that a deal has been concluded, as where you get through the checkout at a supermarket and have paid for the goods. You would not expect in these circumstances for the seller to be able to pull out.

What are the similarities and differences? Why not as when? The relative adverb modifies [the exact time that] 'a deal has been concluded', which is NOT 'a place, location, or space' as required below?

• (Source) "The relative adverb when is used to modify a noun phrase of time. Such noun phrases include nouns that denote periods of time such as, day, week, hour, minute, month, year, and similar events.


• The relative adverb where is used to modify a noun phrase of place, location, or space.

Answer

Where can also be used to indicate a situation, rather than just a location. The same goes for there; it is used to indicate a location, but by extension also a situation, a description of what happens, rather than the exact place where it happens:

Imagine a situation where the customer refuses to pay.
We have all been there: it's your friends birthday, and you forgot about it.
So, what about the case where more than one person shows interest in the offer?

Have a look, for instance, at this well-known idiom (from Cambridge):

where there's a will there's a way
(saying) used to mean that if you are determined enough, you can find a way to achieve what you want, even if it is very difficult

Notice that in the explanation, if is used with this meaning: when you want it, then it is possible.