The two flavors might be very similar, but just like the tricky properties of fennel/anise/licorice root make one mistaken for another, not all cinnamon boasts the same bark.
First, there's cassia. These are the super-hard sticks we find in the grocery store under the label "cinnamon." While a close plant relative to ceylon, it's not the same thing. Cassia is much harder than its counterpart, has a stronger flavor, and it contains a toxic component called coumarin (which shows up only in negligible amounts in ceylon).
Ceylon, or the real stuff, is softer both in taste and texture. This isn't like the stick that could break your spice grinder. You can easily crumble ceylon in your fingers and make powder. It's gentle, yet distinct. Unfortunately, since it's a weaker flavor, it either gets added to cassia, or replaced by it, in the bottled powders we all buy.
If you get a chance, pick up some ceylon and see the difference for yourself!
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