Well one thing they changed is "we're too lazy to make the kernel run in so many modes, so we'll just stop supporting some of them".
They likely optimized it for the 386 so it would run better, and thus there was no point in backporting since the other version was already optimized for a 286 as good as it could get. WFW3.1 is likely a backport of the networking features from WFW3.11 to a version of Win3x that supports 286 mode still.
Edit: Oh, and WFW3.11 was supported until like 2007 for embedded deployment, so it may have had a few network tweaks here and there while WFW3.1 was likely dropped far sooner. WFW3.11 enjoyed an extraordinarily long embedded lifespan, nearly double that that XP did as a desktop OS which was quite long as well. All of this makes for a goldmine of awesome for those like me who enjoy Win3x.
They likely optimized it for the 386 so it would run better, and thus there was no point in backporting since the other version was already optimized for a 286 as good as it could get. WFW3.1 is likely a backport of the networking features from WFW3.11 to a version of Win3x that supports 286 mode still.
Edit: Oh, and WFW3.11 was supported until like 2007 for embedded deployment, so it may have had a few network tweaks here and there while WFW3.1 was likely dropped far sooner. WFW3.11 enjoyed an extraordinarily long embedded lifespan, nearly double that that XP did as a desktop OS which was quite long as well. All of this makes for a goldmine of awesome for those like me who enjoy Win3x.