>but still the spec literally hands you a schematic. Is it that hard to just copy it? Why did they even try to be clever and use their own design in the first place just to save a single 5.1k ohm resistor?

See also: People who like to get all creative with encryption library implementations in commercial settings. If implementing a standard protocol, unless you have a very good reason otherwise, you should;

1. Go and find the guide by the people who designed it.

2. Read the guide and make test thingies till you are sure you understand it.

3. Now go and do what the guide tells you to do.

I can give the automotive electronics perspective here. Suppose that resistor costs 2c, including the actual part cost, PCB space, pick-and-place machine time (inc. more frequent spool replacement). Further suppose you expect to sell one million of this device.

$0.02 x 1E6 = $20k

If you are the circuit designer making, say, $150k, you just justified about a month of your salary (after accounting for benefits and other overhead). Your manager may parade you in front of the team at the next big group meeting as an example of how to achieve the BOM efficiency the company need to hit profit margin targets.

I've never bought into that reasoning on the automotive side. Selling "one million of this device," as you say, will bring in $20 billion. So yes, they can afford $20K to do the job right.

Also, SMT resistors at that quantity level are more like 1/10 of a cent, not 2 cents, and the PnP machine is running anyway. In fact you often end up using more resistors than strictly necessary, just because the machine holds a limited number of reels and it's cheaper to use more of the same part to arrive at a desired value than to add a new line item.

Things should be as cheap as possible, but no cheaper. Optimizing the cost of individual resistors is almost always a classic example of measuring the wrong thing. We should strive to avoid making excuses for doing that.

If it was purely about saving costs why even use USB-C, though? They could have just said that a 3A micro-usb supply is now required for USB power. The Pi4 isn't actually using any of the increased power delivery provided by USB-C PD, which is in the higher voltage range, after all. It just wants 5V 3A, which micro-usb can certainly handle as well (there are a variety of such power supplies for previous Pi's in fact).

Seems like a really questionable cost-savings maneuver to switch to a way more complicated & expensive connector for nearly no reason, and then penny pitch on one resistor.

Costs taken into consideration sure, but the Raspberry Pi Foundation is a charity, so I'm not sure the same sort of incentives exist on a personal basis. It probably is just the engineering attitude of saving costs as much as possible.

Those small SMD resistors come on a reel, and they're typically much cheaper than 2 cent: more like 0.1 cent. Still, that's $1000 for one million units.