I really don't understand why you're arguing points I never made and that aren't relevant. For one thing, you're ignoring the fact that DDR3 came out what, about a decade ago? Thus you could safely upgrade (and I have) with the same RAM for the last decade or so if you had DDR3 back then without (generally, especially in the AMD world) worrying about the MB at all.
I've been upgrading machines like this for almost 30 years. I've had the same RAM in both my boxes for the last 3 or 4 MB/CPU upgrades. I've replaced CPUs without updating the MB several times and even occasionally updated the MB without upgrading the CPU or RAM in order to change up the number of SATA ports and update the USB ports. I've also replaced virtually the entire internal workings at once before, but it's certainly not necessary in every situation.
What you need to replace depends entirely on what you currently have and what you want to buy. I never said otherwise. My point is it's totally feasible to only replace one or two parts at a time (again, depending on what you own and what you want to upgrade to), NOT that it's the only way to do it or that you don't sometimes want or need to update more than one component at a time. Yeesh!
Maybe I just give people more credit than you do. I assume they know that if their MB only supports AM3 and the CPU says it requires AM3+ that at the very least they should look up whether or not they can put an AM3+ CPU in the AM3 socket on their current MB. I assume that if I (and many others) could figure this stuff out without too much difficulty in the era before the Internet was a place where you could efficiently look things up in 3 seconds like you can today, that surely modern users can use Google to find answers and won't just start jamming parts together and hoping for the best.
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I often keep old parts for troubleshooting. It's nice to have an extra PSU or graphics card lying around so you can test things out and know what you really need to replace. I also like old parts because I can let the kids rip them open to see what the inner workings actually look like on some of the old mechanical pieces.
<edit>Apologies for sounding (and being) grumpy - I'm writing this while taking a break from debugging something and am in a bit of a mood apparently. Sorry
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