Actually the Princesses combine the features of Pegasus Ponies, Unicorns, and Earth Ponies. Earth Ponies are stronger, and non-unicorns have their own 'passive' magic, (such as Pegasus Ponies being able to stand on clouds, and it's implied earth ponies have some connection with the earth).
Also Fluttershy is a tree and Applejack is made of dark matter.
Yes, the general consensus is that Twilight was being a very bad scientist in that episode, trying to prove herself right as opposed to trying to discover what's actually happening.Ultratwinkie said:5. Pinkie sense is suddenly scrutinized by science from twilight, but everything else wrong with MLP isn't? Oh yeah we totally know ponies can fly and perform magic. That's science right there.
Also Fluttershy is a tree and Applejack is made of dark matter.