This is something that I've been seeing on older ubuntu versions, too. I bought a new laptop recently and am seeing the same old thing.
It's Asus K53S with i7 2670QM processor, 8G ram and a somewhat slow HDD (5400rpm). While surfing the web with ~5 tabs, on windows, my core temp is on avg ~51C, and on ubuntu it stays at ~56C.
When installing new software etc it gets higher, but I guess it's something to be expected.
Any ideas why the difference and can I somehow lower it (without undervolting)?