Moffat is more interested in abstract concepts like identity, perception, and memories. He also appears to be endlessly fascinated by love and the various ways it can express itself. These ideas can seem less "IMPORTANT" (with a capital I), because they have more to do with individuals than they do with society at large. However, I don't think they are any less valuable.
Also, neither writer sticks strictly to one style. RTD frequently incorporated themes of belief and faith into his scripts (Gridlock or LotTL are good examples), which are rather more abstract than say, the political satire of Aliens in London. And Moffat has dabbled in political satire (The Beast Below).
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