Yea the big difference is going to be to look at the whole picture. Fe-dom and Si-dom respond in very different ways. When I talk about worrying about bad things happening, that is a part of the makeup of the ISFJ. Because of their Inferior Extraverted Intuition. Where the dominant Ne-type can judge the possibilities their unconscious throws out about the world, the ISFJ/ISTJ can't because the inferior operates largely out of conscious control. So all they get is a barrage of "what if this happens, or what if that happens, or what will happen if..." with no real filter like an ENFP or ENTP would have. It actually is the defining characteristic of Si-doms. The MBTI tries to say that Si-doms are traditionalists or stick to what they know, but this would be because of their Inferior Ne not Si. Si is just sensation, a way of perception where what they get out of an experience is more important than the details of the moment itself. Because of the initial orientation inward, the Si-dom needs Ne to help remind them that things might not be as they are perceived. That just because you got one thing out of a perception doesn't mean that's all there is. The problem is that because Ne, for Introverted Sensation types is the inferior function, those possibilities will likely manifest, to the person, negatively (the worst will likely happen, therefore I'll stick to what I know). This is why Si-doms get the stereotype of playing it close and not liking to venture too far from what they know works. They often have very rich inner personalities and can be quite eccentric inwardly (you can think of Si-doms as having an inner ENFP) but the inclination will be not to express this outwardly all that often.
Fe-doms on the other hand get hung up over thinking. Sometimes people may wonder if a Fe-dom has any brains at all. Tim Tebow is a good example of such an ESFJ where he is so oriented toward Feeling (and expressing his values, making sure everyone knows his values), people are forced to wonder "well what do you think for yourself?" This is the nature of Inferior Introverted Thinking. Because the Fe-dominant is so oriented toward externally set evaluations, which depending on how you're socialized might manifest as an adherence to social rituals, their own thinking on those matters gets downplayed. To the Fe-dom "what I think is unimportant relative to the norms of the group." They might have a thought and then quickly downplay it and say "well maybe I'm wrong and everyone else is right." The end result of this is a sort of built-up inferiority complex around Thinking that then goes to define the ESFJ/ENFJ. It's their weak spot and touchy area. Von Franz talks about a Fe-dom student she had who, when Von Franz asked the student to make a small revision to the otherwise excellent paper, the student broke down in tears and said "oh it's all rubbish, i'll tear it up and start again!" This extreme reaction to a minor criticism about the student's Thinking shows the type of hypersensitivity that Feeling types have about their Thinking. I myself as a strong Feeling type have had similar situations where I've made something and then someone gave a minor critique and I threw it all away.
Now mind you this doesn't mean Fe-doms aren't intelligent. What it means is that because they have oriented themselves to the group their Thinking is neglected and repressed (just like a Thinking type represses Feeling and you might wonder if a Thinking type has any Feeling or values at all). But say something happens to a friend and its their fault. Now the Fe-dom will likely be compelled to perform some social ritual (like sending flowers or going to visit them in a hospital or whatever) because that's sort of Fe on autopilot. But they rarely ever stop to think, "Is what I'm doing logical?" "Does it make logical sense?" THis is what we mean by downplay of Thinking. That the preference will be toward making a value judgment (Feeling) over conceptual coherency (Thinking).
So now you can see the difference between ESFJ as a judgment type making decisions largely based on Feeling evaluations, versus the ISFJ who is a perception type caught between a personalized impression of the world and the, often scary, possibilities of what it might become.
I could be dead wrong, though. Most extroverts do have what is stereotyped as "introverted" tendencies. Sometimes Extroverts are quiet and shy. But anyway, onto the functions. 
