The cells in the right column of the table shown in figure 4.5 have different leading or padding. Observe that the default leading of the content of a cell in text mode is equal to the font size. Internally, the leading is set like this: This is different from the default leading of a Phrase object outside a PdfPCell.
There can be a lot of differences between a UDF and stored procedure, as the prior link has shown. Another difference is the UDF can be directly selected from, whereas a stored procedure requires one to insert the results into a tempory table or table variable.
1. That's how a stored procedure works. A SQL stored procedure can only return a single value as RETURN, and it could have OUT parameters. The return value from a stored procedure is different from the ResultSet(s) it could maintain opened when being called, but this is database engine specific.