Comics traditionally come out every month.

Yeah thats what I would have thought but it looks like batman was a bit more varied.

The wikipedia page give their schedule as:

• Quarterly: #1–5
• Bimonthly: #6–80;
• Eight times a year: #81–168
• Nine times a year: #169–177
• 10 times a year: #178–237
• Nine time a year: #238–246
• Seven times a year: #247–253
• Bimonthly: #254–259
• 11 times a year: #260–270
• Monthly: #271–715 except for biweekly status for #436–439, 448–453, 464–469, 477–482, 492–497, 627–628, 643–644, 660–661, 682–683, and 691–692