In fact it was only this year when I upgraded a work colleagues personal laptop from 2GB to 4GB.
Downvoting is an accepted method of disagreement on HN. It's a problematic stance IMO since downvotes grey out the text, making dissenting opinions impossible to make out if they're unpopular enough.
Back on topic, 4GB laptops are incredibly common, especially in retail stores. Getting a laptop with 8 GB of memory frequently requires looking online (most folks still buy their computers from retail stores) and customizing your order.
For example, I just visited both Dell and System76, and except for the gaming laptops, all of them default to 4GB of ram, and adding more (while not terribly expensive) requires thought and action on the consumer's part.
but it seems weird, because Chrome is such a memory monster (it usually takes almost all RAM memory you have on your machine and additionally disk space if you are running of RAM). I have 16GB ram and Chrome takes me 10GB of it and ~1GB of disk space.
As for the 'flag', that's not the same as downvoting. Or at least shouldn't be used in the same way although I have lately seen a disappointing number of comments marked as "flagged" which shouldn't have been. (There's some guidance about flagging posts here: https://news.ycombinator.com/newsguidelines.html). Downvoting is something that's only available to members above a specific karma threshold (2000 IIRC).