and by adding water, you are NOT falsely changing the gravity, you are actually changing it...lowering it a little, because water has a lower gravity than wort.
adding water dilutes gravity, boiling to cause evaporation increases gravity since only h20 evaporates.
it is normal to shoot for 5.25 gallons to accomodate the loss during racking, but its easier to do that in All Grain brewing since you're not stuck with set quantities of DME or LME (or rather, its easier to tailor a recipe to give you 5.5gallons into the fermentor by adding a smidge more grain and water)
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10