The DCX3510-M you purchased at Future Shop would have been a Shaw-branded STB, so that was part of the inventory of Shaw-authorized boxes in place at the time of the Rogers takeover. Shaw used to sell their boxes through certain authorized retailers including Future Shop, Best Buy, London Drugs and Visions.
Shaw was running different software on the DCX3510-M (HD Guide) than they did on the DCX3400-M, so Rogers may have decided it just wasn't worth the hassle since there probably weren't that many boxes installed and they didn't want to support the head-end requirements and the software running on the STB.
In the end it's up to Rogers if they support the DCX3510-M. It doesn't hurt to ask again.