Ars Technica brings an interesting article based on an interview with President of Square Enix, Yoichi Wada. In the interview he states that there is a cycle of buying a new company every two years. In 2003, the two largest RPG houses merged to create Square Enix. Two years ago, they purchased Taito and the Space Invaders franchise.
They go on to speculate their top three suspects for the acquisition; Level 5, NIS, and Tri-Crescendo.
Additional Sources: Next-Gen Biz