I believe this to be an intentional change to prevent holy paladins from spamming holy light on a beacon target then Light of Dawning for very cheap, effective aoe (and even tank, given beacon) healing. I saw this nerf coming because I agreed that it was a pretty ridiculous way to approach Raid healing. Likely also intended to limit the ability to spam holy light and word of glory on a tank for cheap tank healing as well.
That said, the nerf does make Tower of Radiance a very weak talent as far as I'm concerned. In a game where we're encouraged to use our cheap heals as much as possible, having it not synergize with the talent makes it limited in effectiveness. I'd like to see Tower of Radiance reworked to be an interesting talent, but I'm not feeling crippled here. I simply feel like the overarching design of Holy Power for Holy-specced paladins is taking a hit.