I think that we still are not (unfortunatelly) in the times when XP is dead and you can easily ignore it
From what I know, XP is used mostly in the corporate market, not consumers market. If you bought a PC in the last 4-5 years, you probably don't have WinXP. In that sense - XP is dead and gone.
And if XP is gone, DX9 is gone.
Which leads me back to the conclusion that beginners should treat DX9 as deprecated, and just stay away from it.