we do not know the nature of the limited range. it could be anything. including Stellar Drift, since the SGU gates do not have DHD's, which also power the gate, so power is a potential limit.
Power seems the most likely to me, but it doesn't explain why Destiny can't dial further. i'd say that it's the stargates limiting destiny in the form of the galactic identification method via the Gate Remote. the gates emit a signal but that signal isn't very powerful because the Gates have limited power