Vertical text alignment in tabular is wrong

According to http://en.wikibooks.org/wiki/LaTeX/Tables ('The tabular environment' paragraph), I would have expected to be able to use 'p', 'b', 'm' to define vertical text alignment for a column. This Problem with Table Vertical Alignment question from 2010 tells otherwise and provides (a bit inflexible) workarounds.

My question is, if there is something simple to vertically (top, bottom, center) align text in a cell?

Here my code (which aligns 'middle, middle, top', i.e. 'p b m' doesn't work at all...):

\documentclass[10pt]{article}
\usepackage{array}
\begin{document}

\begin{tabular}{|p{4cm}|b{4cm}|m{5cm}|}
\hline
xxx & ab cd ... & ef gh ... \\[10ex]
\hline
xxx & ij kl ... & mn op ...\\
\hline
\end{tabular}

\end{document}


(I also tried with \parbox and \newcolumntype to no avail, \multirow could be an option but didn't try out yet).

Edits: I'd like to achieve the following (as simple as possible;):

-----------------------------------------
| xxx       |           |               |
|           |           | ef gh ...     |
|           | ab cd ... |               |
-----------------------------------------
| xxx       | ij kl ... | mn op ...     |
-----------------------------------------

-

You say "it doesn't work" but you did not say what effect you wanted. Your table cells are single line entries so aligning on the top or bottom line of the cell is the same thing, hence p and b work the same way. The reaction between m and \\[10ex] is slightly caustic but the behaviour of \\[10ex] in tables is fairly weird at the best of times.