Timmee,
Typically any pain experienced in case of inner ear infections/colds and/or eustachian tube blockages will be more noticeable whilst descending while the gases are trying to escape the body.
Not correct. The problem for flyers is that the "gases" ie the increasingly dense atmosphere is trying to get IN, not escape. If the eustachian tube is blocked eg a cold the eardrum collapses inward, causing the pain. When you get the eustachian tube open somehow eg yawn, cough, chew, air is let into the middle ear and and all is equalised.
The system is programmed for around 300-500 feet per minute on descent which is quite comfy for the pax.
I don't know where you get this idea from: 500ft a minute is quite harsh as far as I am concerned. For someone who very rarely flies (like some of these "new" Virgin pax) 500ft per min could be a real problem, and that doesn't mean only if they have a cold. If you asked joe public how they defined a cold, they would probably say in bed on panadol: that's a far cry from what we know can cause big issues with ears in aeroplanes, especially if the standard rate is 500ft per min. A simple runny nose without the correct ear-clearing procedure down the hill will cause problems.