It seems like game designers who work on DnD really have no idea that there is a difference between a +2 bonus to a roll before or after you see the result on the die. In our last 4th edition session we had a Psion in our group who used the ability Guiding Shot which is an immediate reaction encounter power that lets you turn your own or an ally's attack from an attack targetting AC to targetting Reflex instead. You can use it after the attack is rolled though so it ends up being extremely good. Initially we thought it was a Psion ability and were pretty convinced that this alone was able to lift the Psion from a poor class to midrange - after all, this ability is worth 20 damage in the majority of fights we get involved in. Most of the time this ability is worth about +2 to hit but since we make a large number of physical attacks it ends up turning a miss into a hit the great majority of the time since we just wait until we *barely* miss to activate it.
It turns out this ability is actually a power available to anyone with Perception who wants to give up their level 6 Utility power to get it and that probably Psions are just bad since all kinds of classes should be picking Guiding Shot up. Obviously Level 6 Utility powers do something and it is easy to imagine they are better than 15 damage (20 damage that works most of, but not all of the time) but still this is a strong ability even though it only gives somewhere between +0 and +5 to hit.
I looked at this power and then went through my other options and found that many of my choices gave the same sort of bonus: +2 to hit, +2 to damage, +2 to AC, occasionally several of these, and lasting for 1 round. Unfortunately they all required using the ability before the attack is rolled! These end up being worth something like 2 to 4 damage depending on the ability because most of the time the attacks involved end up being hits already or missing by more than 2 anyway.
How can these people not notice this? A +2 to hit *before* the attack is a minor but useful bonus while A +2 *after* the attack is worth almost an entire extra hit! The same sort of thing comes up with the Human and Deva special bonuses which give +4 or +1d6 bonus to hit after the roll. A racial bonus that gives 75% of an additional attack every fight is worth something like 15% extra damage, and can be even more if you have daily attacks that hit single targets and are particularly devastating.
I noticed this tendency for people to completely misunderstand the nature of informed vs. random choices years ago when I was busy posing the Monty Hall problem to various relatives and friends and being astonished that aside from those people in university level mathematics programs the success rate was something like 5-10% to answer the question correctly. People in general just don't understand the impact of prior information on making choices. In the case of the DnD abilities in question it would be reasonable to give any ability that is used after the roll a +1 benefit and any 'equivalent' ability used before the roll a +7 benefit and call them the same. Oftentimes the +1 simply won't come up or will be used at an inappropriate time since we don't know the exact number we are targetting. Instead the designers generally make the bonuses similar in size and render one category of bonus supremely powerful and the other nearly worthless.