It works just damn smooth because of SSD, much better than my iMac with 4GB and faster CPU but regular HDD.
2 GiB is a ridiculously small amount these days, 4 GiB is not a lot on today's standards. A 4 GiB hard limit for max memory is definitely a minus for the computer in question.
For most cases when people claim they need more RAM the actual bottleneck is I/O rate which is kinda improved by having RAM to use as cache, but SSD usually works out even better.
I have no idea why it takes so much memory and I consider it to be somewhat a problem. However, it's not a problem I can do anything about but I still have to live with it daily and get my job done.
Linux has excellent caching for I/O operations, so having more memory makes things faster, so even if something does not explicitly need the RAM, having it there will make thing s go faster.
You need to swap our more than 200 MB per second to saturate SSD in MacBook Air, it is hard to produce that much of non-garbage data.
Plus RAM is ridiculously cheap; I've just seen 24Gb for £100 plus VAT.
RAM is cheap, but it still would take additional volume inside of laptop + use more power.