Until recently, Apple RAM was so overpriced that I'd place simultaneous orders for a minimum-RAM machine and Crucial RAM at the same time. I wouldn't really upgrade an old mac.
I did this only because Apple didn't sell the 4-slot 27" iMac populaed with 4x8GB (32GB) - max BTO was 4x4GB so I got 2x2GB and threw them away and put in 32GB.
Other than that, the Apple ram is not so expensive that it's worth dicking around with making sure you have compatible speeds/pins/size imho (unless you are going Mac Pro in which case the difference on, say, 64GB or more would really add up).
Basically I just don't worry about stuff that amortizes out to under $500-1000/year. (e.g. an iMac for me has about a 36-month useful lifespan)
I blow $220 a lot more often than once every three years (the frequency with which I buy a computer), and on things a lot less important and time-consuming than swapping RAM.
I'm willing to pay some premium for Apple RAM, particularly if I'm not the end user of the machine. I also buy AppleCare for laptops, and AppleCare+ for iPad/iPhone devices, and increasingly, just get AppleCare for desktops, Mac Mini, etc. too. (I used to just rely on Amex Platinum 2x warranty extension, but that's a more annoying process than being able to just take it to the nearest Apple Store for OS or hardware diagnosis and repair.)
The purpose is to have a single point of contact for repair. Not having to personally figure out if the RAM is defective on someone else's machine is a big plus for me. Being able to have the entire thing drop-shipped directly from Apple to the user, also. It depends on the premium -- for a personal Mac Mini, I'd probably do the RAM through Crucial for $50-100 savings or more. If Crucial didn't exist, and I had to go hunting for "good" RAM every time, I'd probably go Apple for $200+. (it is so fun getting a $200k box of RAM for servers, especially left on a porch with no signature required, though. The actual RAM/chip distributor in Fremont that had an 18 person triad armed robbery a few years ago was amusing.)
The annoying part of all of this is that there are some machines where you must pull the drives before any warranty service. The correct thing to do is to have an Apple service rating internal to your company (it costs $200-300 I think, and not much training), but I've never gotten around to it. Lack of swappable externally accessible drives is one of my only complaints about Apple hardware now.
(OTOH, my personal 2010 MBP 17 actually has Crucial RAM, a Crucial SSD 512 in an optical bay adapter, and a 750GB drive in the main bay, all aftermarket. The Crucial drive failed and required repeated disassembly and RMA and firmware loading on another machine, which consumed about 4h of my time, which kind of sucked, and makes me a lot more likely to stay 100% Apple in the future.)
Other than that, the Apple ram is not so expensive that it's worth dicking around with making sure you have compatible speeds/pins/size imho (unless you are going Mac Pro in which case the difference on, say, 64GB or more would really add up).
Basically I just don't worry about stuff that amortizes out to under $500-1000/year. (e.g. an iMac for me has about a 36-month useful lifespan)