Windows based laptop or not, you generalized 'a laptop' and 'a desktop computer'. 'A' pertains to any particular or certain one of a class or group, so I took it just as that.
Now if you said MBPs are for portability and iMacs are for home usage, I'd have no problems with that.
Like I mentioned earlier the OP was about MBPs anything I am commenting on is pertaining to the subject matter of the OP. Perhaps next time I should spell it out with more specifics.