The thing is that Madden after all these years still doesn't make a difference between 4-3 and 3-4 defenses, so all players are rated by the same standards, meaning an OLB gets high OVR from high pass rush AND high pass coverage skills, and DEs get measured by run stop AND pass rush skills. So most 3-4 OLBs are good pass rushers, but not good at coverage, so moving them to DE simply takes their cover skills out of the equation, making them look better.
In the end, it's putting lipstick on a pig, it doesn't really matter since the OVR of players doesn't matter. If you run a 4-3, I don't care how great a pass rusher Aldon Smith is, his 50ish cover skills make him pretty unusable to me as a LB even if his pass rush skills give him a good OVR rating. At the same time, there are many 4-3 DTs in the game that are great run stoppers with a bit of speed, so they're perfectly suited to be DEs in a 3-4 but the game won't give them a good rating because they aren't great pass rushers, which again doesn't actually matter ingame since you'll get your pass rush from your OLBs if you run a 3-4.
So the lesson is, don't just jump on a player because of a high OVR, you need to actually look at his skills to judge how good he will be on the field. At the same time, a player doesn't magically get better just because you move him to another position. Moving Reggie Bush to WR may give his OVR a boost, but again, lipstick on a pig, he's still the same player with the same skills. There's no need to edit his position, as a HB, you can just put him on your WR depth chart or formation sub him if you want him to line up wide. Actually, if you play franchise, it's better to use him in a position where his OVR is lower, because it will allow his skills to progress further.