eBay either did not place enough importance on transaction problems where the buyer wanted an exchange or replacement, or put it in the "too hard" basket. It's disappointing for me as a seller, too - there are two features I want on eBay right now more than anything else (and I mean these as new features, since if I included fixing things that exist but don't work properly, the list would be longer), and one of them is a proper exchange or replacement function when a buyer opens a request, because 90% of the time that's what is preferred by both the buyer and myself.
The thing is, requests aren't the only option, they'e just the only option officially mediated by eBay, if you can all it 'mediation' since a lot of it is automated. Realistically, however, it is not uncommon or completely unreasonable for a seller to require return of the original in order to facilitate an exchange - it's actually mandatory in B&M retail, i.e. you wouldn't be able to just take a receipt into a retail store and tell them they gave you the wrong thing and expect to be given the correct item; you'd need to give back the first item.*
In online retail, what is generally standard practice is for there to be no out of pocket expenses for the buyer when the error is 100% the seller's, which can either be in the form of providing a postage-paid option, or reimbursing any costs to return. There are a number of overseas sellers who are aware this kind of expectation can't be immediately enforced, though, and use the expense and hassle to their own advanatage, but opting into PayPal's funded returns program can at least mitigate the cost of returning something if the seller is being difficult (up to $45 per return, limited to 6 a year last I checked).
*There are possible exceptions to this, of course, and it may even be common in certain types of industries like restaurants or fast food, but it's not standard for most retail outlets.
