Remember Byrna that no matter how hard they try (and the PMDG 737 NG is quite amazing) it's still not like sitting in the flight deck of a 737. It doesn't smell like one, it doesn't vibrate like one, the view is very different. In the real 737 you sit 'in' it, and your arms and legs connect to become part of the machine. With FS you're still sitting in front of a PC.
In many ways, these lack of visual and psycho-metric cues that real world pilots have mean that flying accurately in FS is harder than it is in the real world, plus most FS aircraft are over sensitive in pitch. A real 737 is pretty stable. Once it's trimmed it'll stay where you put it.
Imagine a PC simulation of a Ford Focus. You're driving your simulated car down the motorway at 75mph. It might feel real. Then get in a real Ford Focus and drive down the motorway at 75mph. It's a totally different ball game!