Someone Somewhere said:
If you need high-quality prints, aftermarket ink/toner generally is a bad idea - the quality is typically subpar. This can depend on the exact toner you use, but if it's very cheap, it's probably for a reason.
My guess would be that toners for which a separate developer is not sold either include it in the toner, or it stays in the cartridge even when the tonere is removed. It appears to be just a carrier.
I researched more about developer powder, which is usually iron filings that magnetize the toner onto the developer roller. Some printers have this, usually older ones, some don't. Some have a separate chamber for the developer powder, others it's mixed into the powder hence the two links above that confused me showing both methods.
I emailed XEROX and hopefully they'll let me know about my particular printer and also if the developer powder is used up or not when the toner is empty (so I know if I can just refill the toner). I didn't clearly admit that I'm refilling an empty cartridge which might be against their rules and not get a reply from them but I don't know what I could say to warrant asking such questions as if saying like "I'm very allergic to iron...".
Either one person is wrong or it's different for each particular printer, but if you check the following links, one person says that the developer powder is used up and the other says it isn't (for printers that use developer powder. more modern ones don't use the magnetic developer powder). You can just Ctrl+f and then Find 'developer' instead of reading the whole page.
"Printer developers are consumable, their iron-filing content or resin will be used up or wear out. "
http://mindmachine.co.uk/book/print_15_dev&toner.html
"This developer was not a consumable (although some did end up being
fused to paper). It was simply a transfer method between the toner and
the image drum."
http://www.tomshardware.com/forum/16532-3-modern-toners...
Maybe if users were supposed to add developer powder but didn't is why refilling only with toner powder gives cheap refill toner a bad rep for image quality. I'll take the chance, saves money and resources not needing to produce another whole cartridge. I'll try to post what XEROX says about if this phaser 6180 needs developer powder etc. If they don't reply, I'll just add the toner refill and assume the machine doesn't require developer powder.