This took me a while to figure out too; in addition to seeing different behavior for different users on a site, I saw different behavior for my accounts on different sites. What gives?
The size of the slices shown in the graph depends on how long you've had the account:
If the account is 4 years old, the graph is shown in years. (That's not possible on this site yet.)
If the account is 1 year old, the graph is shown in quarters (as in your first example).
If the account is 4 months old (I think; can't find an example to verify the lower bound), the graph is shown in months.
Otherwise, the graph is shown in 10-day intervals.
Your account isn't yet a year old, so you're still seeing the months view. This should change for you in a few weeks.
You can see all of your reputation by going to the reputation tab on your site or network profile. The small graph on your profile is meant as more of a snapshot, not a complete history.