There can be. Watts are watts but not all claimed watts are necessarily available 100% of the time. In theory, 10 more watts of "engine" power is more likely to be available all the time whereas watts gained from rolling resistance, weight reduction or aero improvements may only be available in certain conditions or not be linear versus speed. For example, if you raise your FTP 10 watts, you will generally have that for the entire ride either as additional power or making a lower power output less taxing, no matter what the conditions. If you get tires that have a theoretical 10 watt rolling resistance improvement that claimed number very likely only comes at a certain combination of speed, tire pressure and road conditions. If you are not in that sweet spot, you may not be getting the full claimed 10 watts or even any additional watts at all.