I stumbled across an article that explains it has to do with loose knitting and those floppy ladders in the back. http://www.amyherzogdesigns.com/2013/11/19/why-swatches-sometimes-lie/
In this current project, the sweater body is 6 inches smaller around than I hope it will when its been blocked. My swatch gives me a gauge of 6.5 stitches per inch. My knitted sweater body gives me a gauge of 7.5 stitches per inch. Huge difference! Panic set in a bit last night as I measured and remeasured my swatch. And I’ve done several google searches on the subject to reassure myself that my math is correct and it will all work out after the soak and block. Here’s another article that tells us to abuse our swatch as if it were our sweater to make sure we get correct measurements: http://explaiknit.typepad.com/let_me_explaiknit/2007/05/gauge_swatches_.html
It’s just shocking how different the gauges are between the fresh-off-the-needles sweater and the fresh-out-of-the-sink (wet blocked) sweater! But, I’m starting to gather that my loose knitting style probably has something to do with that difference. While it doesn’t make sense to change my knitting style mid-project, I may try to see if I can tighten up my knitting in the future to see if it makes any difference.