yes, ours are including preliminary and grandfinal games - as does Uni's according to the Uni website:Out of the 300 games, 45 of them (15%) have been playoff or championship games.
wondering if Darren Mitchell might like to ask for that plaque back and express post it the Hogs camp 
In all seriousness though - congrats on the 300 guys and well done on such a successful history!
FTR - the exact breakdown as of today:
Reg season games : 227 wins, 43 losses & 6 draws = TOTAL 276
Finals games: 29 wins, 8 losses = TOTAL 37
just spoke to our league statistician - she corrected the numbers:
300th game played on Dec 20th 2008
Reg season games: 228 wins, 44 lost, 8 drawn. - total 280 (81.43%)
Finals games: 29 won, 8 lost - total 37 (78.38%)
TOTAL games: 257 wins, 52 lost, 8 drawn - total 317 (81.07%)
none of these wins/losses include forfeited matches or cancellations due to weather etc. I'm guessing you don't included Forfeited wins in your 300 total either?