That's like saying: they should just spend $10B to send 1 free Mac mini to all 20 million developers because they'll still have $190B left over, right?
We have no idea how many DTKs were shipped. And sending free stuff out willy nilly sets a dangerous precedent where developers will time and time again demand free stuff.
First, I don't recall anyone demanding that Apple spend $10 billion, and I'm pretty certain there aren't 20 million developers. But if you have facts to support either of those absurd claims post them here.
Moreover, Apple isn't "spending" anything. It is giving out vouchers to developers that can only be used to buy M1 hardware. At the end of the day, Apple will turn a profit whether the voucher is for $200 or $500, and the vouchers will spur sales for a new product.
And finally, you've already used the term "dangerous precedent" as if it means something. It doesn't. Apple isn't the US Supreme Court, and it's not bound by any "precedent." If it was then it would have provided every developer with a brand new M1 Mac free of charge as it did in 2006 when the last DTK was offered. But it isn't bound by anything, and the next time it releases a DTK, it can choose to charge nothing or double, and then provide zero vouchers (which would have been better than $200).
And even if it was bound by some "precedent", what's "dangerous" about it fostering developer and customer goodwill? Is Apple going to go out of business because of this? Are dividends going to be cut for shareholders? Are Mac prices going to increase? Is the stock price going to drop? The answer is no. Your logic is patently absurd.
What Apple should have done in exchange for the $500 is provided working DTK units and adequate technical support with those units. It failed most developers miserably on both counts, and then offered them $200 to spend within around 60 days on returning the units. Had the units worked and developers received adequate support, there would not have been as many complaints. But it didn't. Ours sat on a shelf the entire time because it bricked itself during an update, and Apple was completely non-responsive. Just another example of Apple treating developers like absolute crap.
But the bottom line is this is between the developers who paid the $500 and Apple. If you think that developers are entitled to nothing then take your $200 or $500 voucher and flush it down the toilet. You wouldn't want to set a "dangerous precedent" by compromising your principles in accepting a discounted Mac.
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