Level cap increase every 1-2 years.

[Murugan]

plz tell me how is grinding for sidegrades and grinding for upgrades any different?

They aren't except one destroys content for new and old players alike, while the other allows it co-exist.

The people with rose colored glasses here are those who think people actually play low-mid level group/raid content. People grind to whatever the new cap is and skip over it. The result is your game after expansion IS the expansion, and that is just a silly way to design an MMO when it isn't necessary in order to keep people who have been playing all along progressing.