I'll try to address some of these "unblockables" or "hard-toblockables," across multiple games:
SF4: Unblockables became a thing from programming error. These unblockables did not exist in the first version of SF4 but later became apparent from the later iterations. DWU mechanic in USF4 solved this issue.
Marvel: Yes it is possible to setup real unblockables with high and low due to assist calls. But thats why Marvel games has always been about neutral game. Especially in UMVC3 where there is ToDs. Dont put yourself into the situation and you wont see the unblockables. Even without the unblockables, the ToD's are much scarier. Most setups that are not on incoming means you're resetting them meaning more chance of them getting away [Alpha Counter, Snap Back assist or character, Super with invisibility, ect.]. A ToD is more preferred option. As far as on incoming such as Zero, again this falls into the neutral aspect. Fast games like Xrd and Marvel heavily rely on having very strong neutral game. This is the meta of Marvel. Theres also Firebrand who have unblockable. With or without a block button, firebrands unblockable will work since it breaks guard. Avoid this by killing FB and winning neutral game. Even then, people are now figuring out ways against Apologymans FB unblockable.
Basically dont put yourself into a situation where a possible unblockable can be set up. If you do end up in that situation then you lost neutral game and got outplayed.
Xrd: Eddie/Zato unblockable..which is about 1-2F to block it. Again neutral. But with the upcoming update, it should be a lot easier to block the unblockable. Same with Millia. In fact a lot of GG players are crying because their cheap techs wont be as effective.
If there is a setup that you dont know how to get out of, simply hit training mode, recreate the situation and find ways out of it because its there.
Anymore games?