Jasperak
Adventurer
Ah what? None of the existing classes are getting changed, they are being added to. Saying that adding some builds with no dailies (that existing players don't have to use) is a big change as 3.0 to 3.5 (where, for example, some peoples class skills disappeared, meaning a rebuild) is not true IMO.
We have only seen a few previews so far. I'll wait to see months down the road what 4e looks like when the essentials class books come out.
I understand your point about these limited previews we've seen and not thinking they are a big change, because they can be freely ignored and they won't effect any other characters in existence. But I think the change is going to be the way WOTC deals with new classes. We've already seen changes to the way some class work.
But I guess just like I didn't have to change my 3.0 Ranger's skills when upgrading to 3.5, no one will have to use the essentials version of magic missile. They can keep it like it was before the errata.