yup that's right. the E-300 wasn't very popular to begin with. the E510 would be a much stronger contender.
together with a battery grip... yummy.
The E-500 was popular. No grip.
The 510 probably will be popular, but still no grip.
If we're lucky the 510 *may* sell enough units for a third party to fabricate one, but I won't hold my breath.