It's the chipset of the motherboard that determines compatibility. If the chipset only supports 1GB or 2GB SODIMMs, then a 4GB SODIMM (theoretically) won't work. That's why you need to find the specs of the motherboard, to find out what it does support. Although usually the Samsung website and laptop spec sheet tells you everything you need to know which it sounds like you've already checked.
Note that even if you did manage to get 4GB to work, it would still be "unsupported", and may or may not have unexpected problems (like intermittent memory issues on load). Samsung will not help with any issues you if they hear you put unsupported RAM into your device.
As a side note, the reason why 3DS says it only supports 32GB SDHC cards is because 64GB+ SDXC cards are usually formatted to exFAT by default and you need third party software to format it as FAT32. The hardware specs are pretty much the same, hence why it works, although I've heard a few reports of some SD cards only showing 32GB usable space (maybe they formatted it using Windows? I don't remember).
