They probably put the +/- 5% there because of the engine they are using. This particular engine from Toyota is rated at 170hp (Corolla XRS), 173hp (Pontiac Vibe), 180hp (Celica, Matrix), and 190hp (Euro Celica). I guess they all have varying setups to make the horsepower ratings differ and Lotus isn't sure how well the engine will perform in the Elise.

 

The reality of horsepower ratings is that typical manufacturing tolerances leave room for a +/- 5% power difference all the time. The various power ratings on cars sold in the USA are due to different ECU calibrations which produce a median hp rating which is the one quoted. The higher rating on the Euro-spec Celica is because they use metric hp which is the same thing as a ps in Japan.

Lotus uses their own intake manifold and ECU to run the motor and since they are able to produce cars in more limited batches than Toyota it would stand to reason that a little more time is spent in fine tuning it to make a real 10 hp more than the US-spec Celica.

 

I don't know about this car...... for my own taste its smiling at me too much.