What is Online Gambling?

You have to remember that nothing in the game has a dollar value.
Nexon strictly disallows trading game items for money or even NX.
So if you cube your item and it gets weaker, that is not a loss of real world money.
Similarly, whatever you get out of gachapon is equally worthless, whether it is a potion or the latest overpowered weapon.

As I previously stated, this argument had credence up until the point that items with undeniable, set-in-stone cash value (like the Premium Fusion Tickets) were added to the prize pool.

Technically you're using your 1200 cash to buy a cube, not a chance to make your equipment better whatsoever, although it's pretty obvious that that's the only thing the thing you buy does.

I am pretty sure there are regulations against the sale of goods that cause undesired damages under "normal use" conditions. As there is only one way to use cubes, there are no "abnormal operation conditions", and, furthermore all risks of detriment are artificially, needlessly, and intentionally crafted in order to massively inflate demand. Perhaps it may be better if potential locks can be obtained for a reasonable amount of mesos.

It may not be gambling-gambling, as it doesn't result in any tangible payouts, but it does require the input of real money (poker chips may not be real money, but like NX cash, they are purchased with real money, so there's no safeguard in that abstraction). There's no federal law against adults engaging in simulated gambling. In some jurisdictions it is illegal for minors to engage in simulated gambling. Does this mean that, for example, players in Florida will need to pass an age verification to purchase and use Miracle Cubes?
Perhaps the ESRB needs to re-evaluate the game. I know there's enough to get MapleStory to a Teen rating, but, since Gachapon tickets and Miracle Cubes can only be obtained with Nexon Cash, which can only be obtained through real-money transactions (and the "worthless" point abstraction in this case is not as iron-clad as Nexon may think), I wonder if the ESRB might have to push the rating all the way to AO.

http://www.law.cornell.edu/uscode/text/31/5362

In order for anything to be a gamble, you have to make a bet, a wager.

This does not include;
viii) participation in any game or contest in which participants do not stake or risk anything of value other than— (I) personal efforts of the participants in playing the game or contest or obtaining access to the Internet; or
(II) points or credits that the sponsor of the game or contest provides to participants free of charge and that can be used or redeemed only for participation in games or contests offered by the sponsor;

Gachapon and miracle cubes cannot be obtained directly through payment. You pay for the NX, that's the intention of the NX gift card. I imagine because of that, the law recognizes the NX points then as "sponsored". Unless the prepaid cards are specifically for those functions, such as gachapon, cubing, surprise boxes, it's considered a "sponsored event". Again, that's my take on it.

Looks like Nexon is indeed breaking the law. They'll be needing to make Miracle Cubes and Gachapon a Maple-Points-only thing.