Well, my memory could be failing me, but I think most home-targeted clones had the big IBM-style speaker until well into the 386/486 era, when dedicated sound hardware became the norm, and PC speaker sound design was relegated to the role of an afterthought. Those speakers may have differed a little in size, but the physical operation principles were the same (in contrast to the piezo-based devices that started showing up later).

As for what kind of machines game developers were working with, that's anyone's guess, but IBM compatibility was a big issue at the time so they probably tried their best to use original hardware... Sierra had big ties with IBM early on, so I bet their old stuff was definitely developed on IBM machines. There's even a historical photo from Windmill Software (not very big-time compared to Sierra) of a machine given to them by IBM for development 😁

Off the top of my head, I can think of one game that actually sounded better with the PC speaker than with a Sound Blaster... 'Metal Mutant' from Silmarils. It used some weird format of 4-bit(!) digital sound, which was real muddy when played back on a SB, but appropriately clangy and "metallic" on the PC speaker.

I'm pretty sure that they had images of PS/2 machines in most of their material that you found inside the game boxes. The ones that had mail order forms for Adlib and MT-32...

It was IBM after all that asked them to develop Kings Quest for their PCjr.

It's a shame that the PCjr was given 3 voices and everyone else only had a single voice...

yeah, PCjr sound was roughly on-par with consoles of those days.

Graphics-wise too (it was basically a much more fleshed-out CGA, the way IBM should've implemented it in the first place)... it's a shame that Tandy machines were the only clones that tried catching up with those things.

http://www.youtube.com/watch?v=RzvaL7LYIAU

Pinball Fantasies PC speaker sound. Just like in the previous video, the signal goes through the Sound Blaster 16.