When you stroke the path you have to remove the selection otherwise the stroke is cut in half (only the part insides is kept). For the rest, "Stroke a selection" generates a path on-the-fly with parameters that are different from the the ones used in the "Select--to-path" to this path is not as smooth.
In the image below, the red is "stroke selection" (selection obtained by "Alpha to selection") and the blue is "select to path, stroke path", and the red is visibly more wiggly.
Attachment:
StrokeSelection-vs-StrokePath.png [ 58.09 KiB | Viewed 5449 times ]
However if you compare the path from Select-To-Path to the path obtained with Text-to-path, you find that the recomputed path is a bit too smooth (very visible in the bottom right corner):
Attachment:
StrokeSelection-vs-StrokePath-TextAndSelPaths.png [ 5.64 KiB | Viewed 5449 times ]