I believe any pre-postseason playoff game will count in the win total. When the baseball almanacs are printed, the final standings include the results of these games (as well as, all the stats). For example, The Red Sox and Yankees played a 1 game playoff in 1978 (a game I attended). If you look up the season standings for 1978 in the baseball almanac, The Al East looks like this:
Major League Baseball final standings for 1978
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American League</TD></TR><TR style="BACKGROUND: lightblue"><TD>Rank</TD><TD>Club</TD><TD>Wins</TD><TD>Losses</TD><TD>Win %</TD><TD>GB</TD></TR><TR style="BACKGROUND: lightblue" align=middle><TD colSpan=6>
East Division</TD></TR><TR><TD>1st</TD><TD>
New York Yankees</TD><TD>100</TD><TD>63</TD><TD>.613</TD><TD>--</TD></TR><TR><TD>2nd</TD><TD>
Boston Red Sox</TD><TD>99</TD><TD>64</TD><TD>.607</TD><TD>1.0</TD></TR><TR><TD>3rd</TD><TD>
Milwaukee Brewers</TD><TD>93</TD><TD>69</TD><TD>.574</TD><TD>6.5</TD></TR><TR><TD>4th</TD><TD>
Baltimore Orioles</TD><TD>90</TD><TD>71</TD><TD>.559</TD><TD>9.0</TD></TR><TR><TD>5th</TD><TD>
Detroit Tigers</TD><TD>86</TD><TD>76</TD><TD>.531</TD><TD>13.5</TD></TR><TR><TD>6th</TD><TD>
Cleveland Indians</TD><TD>69</TD><TD>90</TD><TD>.434</TD><TD>29.0</TD></TR><TR><TD>7th</TD><TD>
Toronto Blue Jays</TD><TD>59</TD><TD>102</TD><TD>.327</TD><TD>40.0</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>