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I'd say you "see more" in an X mm refractor than in an X mm Cassegrain, simply because the latter has a smaller effective aperture (central obstruction). In addition, the Cassegrain has two reflective surfaces on top of the corrector lens with its two air-glass boundaries. This would affect the overall throughput as well.
Keep in mind that a short tube X mm refractor will have a much shorter focal length than an X mm Cassegrain and a much faster focal ratio, with everything that entails.
I believe what you may have heard is that an X mm Maksutov Cassegrain will rival a Y mm refractor, where X is somewhat larger than Y (as in 6" vs 4"). This stems from the fact that Maksutov designs are inherently well corrected for coma (and field curvature?) and good implementations have very good contrast giving a refractor-like view.
Cheers
Steffen.
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