Not really sarcastic, but I think the essential changes are more than you think (epically if you compare just the printed versions).
Frankly, I'm not familiar with the Pathfinder system, but in all the examples below, Essentials wouldn't change anything about an existing character.
P vs 3.5: One more ability bonus.
4 vs Ess: One choose-able ability bonus.
If you created your dwarf fighter in "classic" 4E, you would have got bonuses to Constitution and Wisdom. If you create an Essentials dwarf fighter, you might want to give him a bonus to Strength instead of Wisdom, but a dwarf fighter with bonuses to Constitution and Wisdom is still a "legal" character.
P vs 3.5: Paladins change casting ability (Wis to Cha).
4 vs Ess: Warlocks are now all Cha based.
Technically, the Essentials Hexblade is a new Charisma-primary build for the warlock, but not all warlocks are Charisma-based because the "classic" 4E warlock builds still exist. If you are currently playing a "classic" 4E warlock, nothing about the Hexblade requires you to make changes to your character, although if you wanted to, you could choose one or more of the new warlock powers introduced in Essentials (those that are not Hexblade-specific, of course). This is the kind of thing that happens all the time in supplements.
P vs 3.5: Revised Power-Attack and similar feats.
4 vs Ess: Gives additional Expertise feats that make older ones obsolete.
Again, this is the kind of thing that happens ... okay, maybe not all the time, but occasionally in supplements. You get a new spell, feat, power or whatever that works better than something similar that has come out before. At least 4E has retraining rules that allow you to replace the old game element with the new one.
Now, it could be argued that Essentials prompted certain revisions such as the change to Melee Training. However, because such changes are also presented as errata, an Essentials game and a "classic" 4E game with the latest errata are effectively running on the same game system.