Well, Thunderchild, there is some historical evidence to support this view. However, there really is no such thing as "Protestant" because it covers so much theological ground. Martin was the first in the Reformation era to challenge the papal teachings. Zwingli and others followed that lead.
By the time of the Augsburg Confession (1530), there were four groups that presented theological papers: Lutherans, Zwinglian, Anabaptists, and the Radical reformers. Interesting that Calvin (1509 - 1564), a later arrival on the Reformation scene, had the greatest influence among Reformed ("general Protestant" for lack of a more precise term) until the late 1800s. Arminianism, a 17th century derivative of Calvinism, which flourished with Finney's help has now become the dominant "popular" expression of the Reformed/Protestant movement. Basically, the "Protestant" movement would be Zwinglian with regard to the sacraments - "symbols only" - Arminian with regard to salvation/free will, and Calvinist in terms of political orientation.
While in popular terms, Lutherans are lumped within Protestantism, theologically, Lutherans would be distinct from the Reformed/Protestant groups, and distinct from RCC and Orthodox.
The most significant difference has to do with the understanding of Law and Gospel:
Law - tells us what to do and not do; threatens with punishment when we fail.
Gospel- tells us what God has done, is doing,a nd will do for us through Jesus Christ.
Sometimes God speaks Law and sometimes God speaks Gospel.
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I think any time we are content with our status, we come face-to-face with God's Law that shows the demand too much - for anyone. We have three options: go away in despair, become self-righteous, or receive the offer of satisfied righteousness of Jesus Christ. Sadly the rich young man in Mark 10 could not come to grips with the ultimate demand, nor God's solution.
Notice that since the man asked a "Law" question ("What must I do to inherit eternal life?", Jesus gave him a "Law" answer. BTW the "Law" answer was impossible to fulfill. It was designed to show him his sin - the impossibility of living up to God's perfect standards.
Notice in a parallel account in Acts 16:25-33, the Philippian jailer asks the same question ("What must I do to be saved?"), but in this case Paul responds with a Gospel answer: "Believe on the Lord Jesus Christ and you will be saved" - same demand, different response. Why the difference? It depended on situation of the one who asked the question. The rich young man was expecting to be given a final few tips to go over the top, so to speak. He thought he was already "pretty good." He needed the Law in its fullness, which Jesus spoke. The jailer, on the other hand, was devastated, knowing that death awaited him. His question of "doing" something was out of despair of anything he could do. Thus, Paul's answer brings hope and comfort through Jesus Christ, not through what the jailer could do.
For us, well for me, that is the difficult part: knowing when to speak Law and when to speak Gospel to someone. Even more difficult is trying to determine what I need! Maybe that is why Martin Luther said that anyone who could properly distinguish Law and Gospel - and apply it - should be a doctor of theology.
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Ultimately when trying to distinguish between Lutherans and other Christians, the discussion begins and ends with an understanding of that Law/Gospel dichotomy.
