Good question - it's hard to tell from the descriptions. I've used both. The DLC-10 comes with a dough blade, an additional flat (non-pusher) cover, and an instuctional video. I rarely use those items - when I bake, I don't knead dough in a machine, and it's just as easy to pour liquids in through the standard pusher cover. The video is well-made and helpful, but only if you've never used a Cuisinart before.
All of that one could tell mostly just by looking at the pictures, but the main two SIGNIFICANT differences are the pusher cover; and the way the accessory blades are used.
First, the cover on the DLC-5 has a wide hole; the DLC-10 has a 2-in-1 design with a large AND small hole - so that, for example, one can slice one carrot in the DLC-10, but not as easily or cleanly in the DLC-5. It would tend to move around and result in uneven slices.
Second, the way the blades attach in the DLC-10 is a tiny bit more complicated, but makes them much more suitable for heavier-duty use. Also, because of this design, the DLC-10 can use the dozen or more standard accessory discs, but the DLC-5 can use only the two discs made specifically for it (although one could certainly buy the $10 adapter stem to use the others).
Bottom line: the DLC-10 is slightly more complex, but more flexible in use and more expandable, and comes with more accessories. The respective models are the exact SAME price (at least today!), so I'd definitely get the DLC-10. (The DLC-10 I bought over 15 years ago and use every day is still working perfectly, so I don't need a new one yet!)
The messages have summarized the differences, but it seems worth noting that some people might prefer the DLC-5 because its cover is MUCH easier to handle and to clean, at least in my experience. The flexibility of having both large and a small feed tube holes comes at the cost of a complicated locking mechanism, with a double sleeve that can be very hard to get food particles out of.