In only the most rarest occasions can a mobo be upgraded. And at that only custom built laptops can really accomplish this. Not to mention within a certain degree of still new laptop. There are only a few end user grade laptops that can change much of anything. His comment isnt really that far from the truth. What you speak of is hardly readily available to most users, even though people like you and me know they exist.
Really though, upgrading wifi? Even in the last few years they shifted from MiniPCI to MinePCIE form factors within laptops and laptops made far enough back have no option to upgrade.
Memory, oh, okay, I can add (in virtually all cases prior to newer DDR3) up to 2 memory chips, of which it likely shipped with both filled (4GB) unless was custom ordered as well? You will still be locked into one memory type and likely adding more to your system like 6-8GB will do nothing for the overall usage of the still older laptop.
CPUs, this is mostly laughable. Lets say you did buy a slightly older laptop with a Core2Duo based CPU, without the aforementioned rare possibility of changing the mobo, you would hardly find it worth it to go from a 2.2Ghz C2D to a 2.6-3Ghz C2D. Though possible, the mostly still older C2D would not make much of a difference in overall use and hardly worth the investment since a new base build laptop would be more efficient dollar to performance ratio. And vastly cheaper than upgrading the one off components.
In short, what I think you are missing from the comment of get rid of the old and just get a new one, is that you will likely recoup more of your investment from the old unit and put towards a new unit, then to try to work with upgrading something like a laptop mobo, which I can tell you (from 20 years of laptop servicing), that the average even PC builder could disassemble a modern day laptop without breaking something, much less the average nontechiejoesomebody. And it is only getting worse, with the latest changes in consumer demand, apple design metrics, and overall tight designs, it is getting harder to break these units open and not show that someone has worked on it. Not to mention if you didnt buy a custom laptop and you want to upgrade something like the mobo, you are likely voiding your still good warranty, and that is a big deal for most users. Without changing the mobo, most of any upgrade is pretty worthless.