The other thing to be aware of is that often the specs are simply stating the highest build to order option, rather than an actual limit. Or, they're listing the maximum capacity (storage or RAM) that was available when the product was released (e.g. 1.5TB or 2TB drives may not have been commonly available at that time).
Do pay a little attention to the tech specs though as sometimes they do reveal real limits. For instance, I had an old G3 that had a limit in its logic board where (if memory serves) it couldn't handle 512mb DIMMS at all and could only handle double-sided 256mb (the single-sided ones used higher density chips than it could address, similar with the 512mb sticks), but considering I think this machine originally shipped with something like 32mb of RAM this was significantly above the original shipping spec.
