A few issuse that I need to discuss.

[Shaxx]

Well, I have spent most of my forum-going experience over on pojo, but I like the DP tier/moveset pages here. While viewing said pages, I have realized that the EV spreads only go to 508 not 510. Is there a reason for this?

 

[Neutral777]

The EVs work such that for every 4, the stat is boosted 1 point.

508 is divisible by 4. Those last two extra points won't affect anything so they don't really need to be used in such a case.

 

[Taylor]

This can be answered in the 'Simple Questions Simple Answers' topic, located on Stark's first page and stickied.

To answer your question: 4 EVs give off 1 stat. Considering that 510 is not divisible by 4 - but 508 is - it's useless having 510 EVs in one Pokemon when the remaining 2 EVs have no effect at all.