I think there's two answers to this:While I would like to play a paladin defender in 4e, I'd also like to play a paladin striker, paladin leader, or occasionally even a paladin controller.
First, classes in 4e are a lot more abstract than they were in previous editions. If you want a Paladin striker why don't you just create a Lawful Avenger and play it as a Paladin? There's a lot less 'baggage' attached to a class's name.
Second, things have become more fluid over time. Classes introduced in PHB2 and PHB3 typically feature (and explicitly mention) secondary roles. Using multiclassing, hybrid rules or - my favorite - appropriate themes will allow you to lean towards roles that don't match your 'primary' role at all.
E.g. in our current Dark Sun campaign I'm playing a Dray (Dragonborn) Dragonmagic Sorcerer with the Templar theme.
Sorcerers are strikers first and controllers second while Templars are leaders. Being a Dragonborn and using the 'Dragonmagic' Build synergizes quite well with Melee classes like the Fighter.
So, depending on what aspect of my character I decide to emphasize when choosing a theme, feats and powers (and later paragon path) I can lean towards any role I prefer. The only thing I probably cannot do is not be a striker.
I generally don't like Essentials classes because they reversed this trend, cut down on customization options and imho focus quite strongly on a single role.