WOW has had some issues with scaling in the past. The best examples of this are dps warriors throughout the history of the game (for scaling too much) and shadow priests in TBC (for scaling too little). Scaling is a word that is horribly abused throughout the WOW community by people who fail completely to understand what it means. "Poor scaling" is regularly used to mean "I am bad" or "My class isn't powerful enough" instead of what it actually means which is that the class in question does not adequately improve given general stat increases compared to other classes. Dps warriors have historically been terrible at the start of expansions and then overpowered at the end because their rage scaled so much. Cataclysm seems to have several reduced this and it appears that rage will not scale out of control this time. Shadow priests in TBC simply gained no benefit from any stat but spellpower and since their first pieces of gear had almost as much spellpower as their top tier pieces they basically never improved at all.
Ret paladins at the moment are suffering from terrible scaling. The main problem is that there are 5 secondary stats - Hit, Expertise, Mastery, Crit and Haste. Hit and Expertise cap out fairly quickly for everyone, so there are 3 stats left. Ret paladins gain relatively little from Crit compared to other classes but aren't really abysmal - just weak. Unfortunately both Haste and Mastery give Ret paladins the same benefit - more buttons to hit to do more damage. The problem here is that Ret paladins are already nearly GCD capped anyway so more buttons is actually a very weak mechanic, particularly when both stats give more Templar's Verdict casts and TV is the third best attack we have. To give an example, say a Fire mage gets enough Mastery to gain 100 dps. Then imagine they gain enough Haste to get 100 dps. What happens if they gain both of those things? Their dps goes up by 220 (guesstimate). Now imagine the same thing happens to a Ret paladin. Instead of getting a 220 dps gain they get a 180 dps gain. The additional procs from Mastery and Haste interfere with each other and cause lost procs, not to mention the fact that Mastery in particular is absolutely trash for Ret paladins.
Right now Ret paladins are behind the curve in damage, not immensely so, but we are on the weak side. This is going to rapidly escalate as we get raid gear and secondary stats begin to pile up. There are plenty of solutions for this problem, some of which will work temporarily and some of which will work for the whole expansion. Blizzard needs to give up on the idea that a class which is nearly GCD capped can scale with two different stats that give them more buttons to hit. Actually making that work would require strikes that do truly immense amounts of damage such that they are worth hitting over whatever else would have been in that spot and that type of strike is going to unbalance pvp dramatically if a string of procs occurs. Since haste is supposed to be the 'do more' stat across all classes that means mastery simply needs to get rewritten. If the amount of mastery gained per point was doubled or trebled it would make it temporarily quite good but long term there would still be problems. Mastery needs to be something passive that simply makes more damage happen, and it could be as simple as a flat damage increase like Arcane mages get or extra strikes that proc like Arms warriors. Whatever it is it needs to get away from the 'more buttons' idea that would work for many classes, but specifically not the class that got it.