As I see it:
"Almighty" means having supreme authority and unchallengeable power. No other being can dictate terms to or foil the actions of an almighty being. However, an almighty being is not necessarily able to create or lift a rock of arbitrary size.
"Omnipotent" means having either all logically possible power or all imaginable power, depending on who you ask. The first runs into problems like whether there exists a particle so fundamental that an omnipotent being cannot split it (so far we're down from atoms, to protons, to quarks...), and if so, who dictated that it was to be this way, the second runs into even odder problems like whether such a being can deny its own existence without lying, and both of them run into problems generally filed under "Omnipotence paradox" (check Wikipedia if you like) and arguments over semantics. Also, saying "God is omnipotent" gets you in trouble with people who want to know why God wasn't powerful enough to create free will without evil.
I disagree. One may debate the nature of omnipotence and run into problems whether or not one cares whether or not there is an omnipotent being.
My answer is "God is not omnipotent".
That's one possible reason.
Doesn't this run counter to what you were recently saying, in that Zeus was clearly not omnipotent?
Since I don't recall saying that the universe is the control of God, I hope you'll understand that I don't feel compelled to rebut this statement.
I think that might depend on the hypothetical power level of this alternate Satan, but I agree with the general principle.
Beware of oversimplification.
And I say that (the problem of) evil does not coexist with (benevolent) omnipotence and that (benevolent) almightiness can coexist with evil because evil is a temporarily necessary means to other ends.
Eran gave the simplified version already, let me quote the Sura I was referring to.
"Those who believe (in the Qur'an), and those who follow the Jewish (scriptures), and the Christians and the Sabians,- any who believe in Allah and the Last Day, and work righteousness, shall have their reward with their Lord; on them shall be no fear, nor shall they grieve." (Al-Baqara 62, not sure what the correct quoting style for the Quran is, also Yusuf Ali.)
If this helps you imagine it: Name me a few religions that do accept Christians into their local good afterlife, assuming that that other religion is true as specified. Now name me a few that don't. Now consider the reverse: following which of those get you to a good afterlife if Christianity is true?
Lazybones. Read the Wager yourself.
Here's the Pensees that it appears in. Section III, last part of number 233.