CLOB is encoding and collation sensitive, BLOB is not.
When you write into a CLOB using, say, CL8WIN1251, you write a 0xC0 (which is Cyrillic letter А).
When you read data back using AL16UTF16, you get back 0x0410, which is a UTF16 represenation of this letter.
If you were reading from a BLOB, you would get same 0xC0 back.