Strava doesn't use normalized power, nor is the difference the difference between a 25-second and 30-second moving average; and I'm pretty sure that "plagiarism" shouldn't be the charge. If anything, Strava avoided using NP because TrainingPeaks had trademarked the name (though not the concept), which is odd since they didn't come up with that name -- I did. I was pretty surprised when I found out that they trademarked a name I came up with.