first off there is no thumb rule as swap = 2x RAM.
these days hdd space is more, back in those days 650 megs of hdd = heaven or dream come true, they were all BNC net or floppy net or net image or some mode or other which resulted in dumb terminals, they had the booting off via NFS root. those days RAM was expensive.
ram's clock cycle is in gigs and before in megs. but hdd's clock cycle is in 3600 then, now 7200 and newest 10000 rpm. so those days also they had to run dbms, and dbms like bdb berkeley db which normally uses a lot of processing and indexing which reqires a lot of ram. so, the rule is valid still today. if you want a database server like mysql or pgsql or oracle or db4.3 or unixodbc? you need an insane amount of RAM. which is why? if you are planning to run dbms? then to be on safe side? 4x RAM is safe and secure from hdd potential crash.
coming to point 2: if you upgrade RAM what do you? STOP being a PANICKY CHICKEN CHICK with skirt. swapoff the swap drive, remove it from fstab, resize some partition where you got loads of space for party, create a new partition for swap and format it as a swap and swapon. rh 7.x got a nice howto on system customisation.
/dev/mem and /dev/kmem = RAM memory and /dev/hdNX = hdd, RAM = high speed hdd. in short and they ease the process of io which is why we have seek time.