Why do commas behave differently in int.Parse() and decimal.Parse() with InvariantCulture?

Why does:

decimal.Parse("1,2,3,45", CultureInfo.InvariantCulture)

return a decimal of 12345, yet:

int.Parse("1,2,3,45", CultureInfo.InvariantCulture)

throws an exception? I would expect the commas to be treated the same for the same culture. If decimal.Parse returns 12345, why doesn't int.Parse also return 12345?