I would guess it's because he has contributed more money, in other words he's spent more on supporter. Just giving people who have given him more money a little extra something to represent their patronage. I wouldn't call Peppy greedy for it unless he starts making "supporter tiers" relate to actual benefits, which would be pretty bad and a slippery slope to say the least. That aside, I don't see either heart on the "old" website, and the new site is still pretty puke.
Cookiezi has 3 hearts for example, but I don't know if gifted supporter counts towards your hearts or the gifter's, I doubt Cookiezi has had to buy supporter very often... if ever.
this is all speculation but I am pretty sure this is what it means.
The alternative is that it is loosely indicating how much supporter time they have left in months, kind of like a health bar. It's not as precise as your own page of course but for example maybe 1-3 months is 1 heart, 3-6 months is 2, 6-9 is 3. Etc.