Apparently Lady Stoneheart isn't there either, her actress isn't in Season 5.
As for Aegon, I'm sure they're just waiting before revealing him. Plenty of season 5 actors are listed as "Role: To Be Announced". If they said "Role: Aegon Targaryen/Young Griff", it'd be a HUGE spoiler and ruin the surprise. As to Varys, it's important to note that he seems to be taking Illyrio's role as exposition dump for Tyrion... and Illyrio never mentioned Aegon to Tyrion, he mentioned Daenerys. Tyrion figured it out for himself during his Huckleberry Finn adventures, so the show's not deviating from the books in that regard.
But, I've seen an interesting theory on the Ice and Fire forums. Some think that Aegon is going to be merged with Trystane Martell, which would explain why he has a prominent role in the show, as opposed to the books where he was only mentioned, never seen.