Vampires, kneeling and the draw of a cute blonde slayer

[sl_podcast]

So rewatching Buffy this time (as I do often)... I noticed that both Spike and Angel kneel in front of Buffy (Angel, right after he returns from hell and Spike, during OMWF).

I'm sure this was purposeful... but I'm not sure what to think the purpose is.... what do you guys think?