I don't know what you mean by "in almost all cases." Commonly, the text of a House bill and a Senate bill do not agree, word for word. Sometimes this is resolved by members of each house meeting quietly in camera
; but yes, a conference committee is often convened to resolve such matters, which are often just a matter of the wording of the text. Of greater consequence are riders--amendments to bills which are added at the last minute, often in the hope that both houses will pass the bill and
the rider or riders just to get it done with.
You're begging your own question--it doesn't become Federal law unless both houses approve it by a roll-call vote, and it is signed by the president. In the event that the president vetoes it, or ignores it (called a pocket veto), then it would require a two-thirds vote by both houses to make it law.