Do Christians, Jews, and Muslims all worship the same "God?"

The following quotation is from the "Adventist Discovery Centre" website.  (http://www.discoveronline.org.uk/about_us.php)

"3. How many Gods do we have?

There is only one true God. As the first commandment states in Exodus 20:2-3
"I am the LORD your God, who brought you out of Egypt, out of the land of slavery. You shall have no other gods before me."

There are many objects of adoration or worship around the world, but there is only one God as revealed in the Bible. This is the God worshiped by Christians and Jews, and is the same God worshiped by Muslims under the name of Allah.

However, as we saw in the last question, God can have many names (and if we look through the Bible we find many given to him, mainly describing his character), so he can also make himself known in different ways.  In the Bible we see God revealing himself in what Christians call the Trinity:  God the Father, God the Son and God the Holy Spirit.  One God, but working and showing his character in three ways."

There are several interesting things about this quotation.  Firstly, I have never read of any Jew or Muslim that professes Christianity's "God" to be the same as their own.  Secondly, "One God," "working and showing his character in three ways" sounds more like a Modalist perspective rather than the "three beings" of Whidden, Moon, and Reeve.

The next quotation is taken from the official SDA website, whatdoadventistsbelieve.com:

"Trinity.  As with much of the rest of Christianity, we as Adventists, are very comfortable with the phrase 'three in one'.   A critic can claim that literally we are therefore not monotheists, that we actually believe in three gods.  But it is one God, with the understanding of a plurality of three.  Father, Son, and Spirit.  We see the Scriptures consistently describing the Trinity.  And the Bible, in describing God, uses all three titles and attributes.  It is complicated, and we do not claim to fully understand this, or feel that we can completely describe the trinity of God.   However, we do think that God reveals himself to us and that he can be known.  Like any relationship, we get to know him better over time."
(http://www.whatdoadventistsbelieve.com/home/Home/Entries/2010/1/7_No._2_-_The_Godhead.html)

A close reading of this statement reveals several startling facts.
1)  Adventists along "with much of the rest of Christianity" are in unity and "comfortable" with the Trinitarian "three in one" doctrine of God.
2)  Critics do claim that Adventists are not monotheists but rather Tri-theists.
3)  Some Adventists understand that God is numerically "one" being who manifests himself as a "plurality of three."  Other Adventists believe  God is a "plurality of three" divine Beings who are "one" in character, purpose, and love.
4)  The Scriptures consistently describe the Trinity.
5)  Yet, the Trinity is so very "complicated" Adventist leaders and members "do not claim to fully understand" this confusing doctrine.
6)  Adventist leaders and members do not feel "that we can completely describe the trinity of God."
7)  If the Trinity doctrine is so "complicated" that we can't "fully understand" or "describe" this confusing teaching:  why make it such an important TEST of fellowship?  Back to point number one:  So "much of the rest of Christianity" beginning with Catholicism, enforces the Trinity as a test of fellowship.  Now, we are finally accepted and fit right in...

“And they forsook the Lord God of their fathers, which brought them out of the land of Egypt, and followed other gods, of the gods of the people that were round about them”  (Judges, 2:12.)