It's cheap and easy to upgrade your laptop from 2GB to 4GB.
It can be expensive to upgrade your laptop from 4GB to 8GB, no matter how cheap the RAM itself is, because you might have to buy a new laptop to accomodate.
It's a much more expensive (and logistically difficult) task to roll out that kind of upgrade across a large hosting environment with hardware purchased over multiple deployments.
yeah... generally when you buy a box for VPS hosting, you fill it to capacity with ram... of late, the price/density of ram hasn't changed much, so usually you'll throw out the box and replace it when it's time for an upgrade.
None the less, new servers with lots of ram aren't that expensive. Registered ecc ddr3 is about $130 for each 4GiB stick, give or take, and that comprises about half the cost of a server with 8 cores and 32giB ram. (on the G34 platform, that's a single socket server)
It's cheap and easy to upgrade your laptop from 2GB to 4GB.
It can be expensive to upgrade your laptop from 4GB to 8GB, no matter how cheap the RAM itself is, because you might have to buy a new laptop to accomodate.
It's a much more expensive (and logistically difficult) task to roll out that kind of upgrade across a large hosting environment with hardware purchased over multiple deployments.