A little reading for you. http://www.ycars.org/EFRA/Module%20C/TLSWR.htm
As power increases, if your antenna is not properly tuned to your transmitter, your SWR increases as well. An SWR of 3 is very bad, and can damage the unit.
Since all these things are mass produced, chances of the antenna being properly tuned to the variances in transmitters is not very good. So chances are, right out of the box, you'd probably have an SWR of 1.5 and standard output power (this is a guess, and that SWR is in acceptable ranges for the normal person, only neurotics like myself try to get the 1.1). The more output power you transmit the better you want to tune your antenna.