If my records are right, the last time I added to the list of MMO's where I have capped a character was back in mid 2012(!). I spent a decent chunk of late 2012 and all of 2013 re-capping characters who were not longer max level due to expansions, but failed to reach the cap in any new titles. I finally broke the streak when I got Cyclops to level 60 in Marvel Heroes around a week ago. The journey there is an odd commentary on exp boosts in the non-subscription era.
Like most non-subscription titles, Marvel Heroes offers exp boosts in its cash shop. You can get a limited number of these in-game; one exp boost and one drop rarity boost per character per difficulty from non-repeatable quests, and up to two random fortune cards (roughly 85% chance of containing a random boost) daily if you farm all the terminal missions and spend all of the cube shards accordingly. They are also frequently thrown in with character bundles in the game's cash store, so I had a fair number of them in storage.
Busting out the bonus potions for the last ten levels was a relatively obvious and easy choice - I spent the last 10 hours or so running anywhere from +50% to +200% in exp bonuses, and thus on paper shaved probably 10 hours off of my leveling time. I had 30 minutes of bonuses adding up to +240% left on the clock when I finished, so I ran some legendary quests on Deadpool and advanced from level 25-29 as the last bonus expired (dropping me down to my new permanent baseline of 40%).
In total, I definitely saved some time, I "wasted" some content (I didn't finish all of the story missions because they are tougher and less exp/minute, and I will need to do some of these later for quest rewards), and technically I didn't pay anything extra out of pocket since I got there entirely through thrifty use of stuff that came with hero bundles I was paying for anyway. I wouldn't say the bonuses were required, but in a game where I will be continuing to repeat the content it's nice to be able to move on to the next objective early.
Nothing here is broken - indeed, they're willing to "undermine" their own exp boost sales market by granting permanent bonuses for your alts relatively freely. (I'm currently at 41%, 42% soon, it's relatively easy to get to the mid 70's with four capped characters, and a player who caps all the heroes can actually have 210% permanently for all new characters that are added.) It's just something to watch for, and something that games that don't use the exp curve as a revenue stream don't have to deal with.
(By contrast, Marvel Heroes has been very willing to add inventory clutter with currencies that don't go in its currency tab, massive variety of relics and boosts that are just slightly different so they can't be stacked, and a new runeword system that will add forty different runestones to the inventory. They are very willing to make it easy to get more characters on which to acquire loot that needs to be stored but very inflexible when it comes to any discounts on storage.)