Don't know who exactly you are asking this of, but yes I agree. Spending $50-100 extra on a "better" motherboard hoping for better performance is just $50-100 down the drain - at same CPU speeds. Now, there is a case for the "better" board to overclock higher, but it better overclock a LOT higher to be worth that much money difference or you'd be better off just spending that much more money on a faster CPU to begin with.
Memory is the second thing that you should NOT spend money on. Let me clarify - you do need RAM and it shouldn't be some ultra-generico-crap, but it does not need to have shiney heatspreaders or LEDs on it and it does not "need" ultra low latency. Sure, looks are important and low latency does add performance, but is it worth the cost difference?
Let's combine the above two scenarios. It is possible to get an $80 motherboard (heck, even the Abit KN8 is available for around that much) and it is possible to get a $180 motherboard. It is possible to get $150 2GB dual channel kit (G.Skill, among others) and it is possible to get $250 pimped out RAM. What will that extra $200 get you? Well, that's the difference between a 7800GT and a 7800GTX. What will give you higher framerates, the expensive RAM/mobo or the faster video card? That's MORE THAN the difference between an Athlon 64 3200+ and 4000+. What will give you better encoding performance, the expensive RAM/mobo or the faster CPU? BTW that 4000+ CPU is a San Diego core with 1MB cache so even if the cheaper CPU can overclock as high as the faster CPU can overclock, the 4000+ will remain faster at same GHz.
Now, if you have money growing on your tree in your backyard or Bill Gates is your uncle twice removed, then cost may not matter much to you, but if you are like the rest of us mere mortals then you cannot afford the "best" of everything, so you have to make your money count.
It comes down to your budget and what you use your system for.
If you are a gamer then #1 concern is video card followed by CPU, then amount (not speed) of RAM, and last is motherboard.
If you do more production work such as encoding but also game, then #1 concern is CPU speed followed by video card, then RAM and finally motherboard.
If you absolutely do not play 3D games, then video card drops from top two on list down to a tie for last place with motherboard.