i saw this pic at yellowjersey and was wondering if there is a non-aesthetic purpose to the slotted bottom bracket shell (other than it makes you go faster, of course)

drainage of gunk?

Water drains out and lets the tubes air out after wet weather.

Something that excessive is probably just for looks, but it does also provide some good drainage.

so you can see the phil logo from your bottom bracket

weight?

It's that way so you can remove all the decals and still let people know that Mr. Nagasawa built your bike. Drainage too.

OK, so I get the drainage thing but if it's that useful, then why is it not more common/standard? It seems like it's just more cool factor and others don't do it b/c, well, they're just not as badazz like that.

It's time consuming and expensive, which is why (in general) only the higher-end bikes have it.

lots of bikes will have a small hole drilled for drainage. If you're concerned about stuff getting in you can.... https://www.execulink.com/~dtierney/wmc/faq.htm#FHQ2

Obviously this sort of thing won't work for cut-outs as pictured, but it looks great for smallies.