That puzzled me as well, but didn't remember to ask about it later. Judging by the early stage of the unpainted prototype (the armour), they probably haven't decided if the Prowl toy will be recoloured. We already know of two recolours of first wave toys (Bumblebee and Lockdown), so a Prowl recolour would be expected.
The problem though, is that the Armor pack version would be early 2009 at the earliest, so would it be worth the risk of holding out on the Prowl from June's release?
This one's a tough one, because nobody likes buying unwanted duplicates. It's kinda like the Cybertron Vector Prime toy, which some had to buy again to get the Starscream toy (in the later released 2-pack set).