Why is that? Shouldn't they both be 2cmx2cm in size?!

\documentclass{article}
\usepackage{graphicx}
\begin{document}
\resizebox{2cm}{2cm}{\rule{6cm}{7cm}}
\resizebox{2cm}{2cm}{\begin{tabular}{l l}A&B\\C&D\end{tabular}}
\end{document}
Why is that? Shouldn't they both be 2cmx2cm in size?!

\documentclass{article}
\usepackage{graphicx}
\begin{document}
\resizebox{2cm}{2cm}{\rule{6cm}{7cm}}
\resizebox{2cm}{2cm}{\begin{tabular}{l l}A&B\\C&D\end{tabular}}
\end{document}
You want \resizebox* not \resizebox the latter scales the height whereas the former scales height + depth. A tabular is vertically centred so the height is half its vertical extent.
I do not know why, but:
1) If you want to have proper dimensions, use:
\documentclass{article}
\usepackage{graphicx}
\begin{document}
\resizebox{2cm}{2cm}{\rule{6cm}{7cm}}
%\resizebox{2cm}{2cm}{\begin{tabular}{l l}A&B\\C&D\end{tabular}}
\resizebox{2cm}{2cm}{\begin{tabular}[b]{|l l|}\hline A&B\\C&D\\ \hline\end{tabular}}
\end{document}

2) If you want to see a horror, please change [b] onto [t]. I know that it is not a proper answer, but one should to see THAT! :-)
parboxandminipagein resizebox while I was trying to construct an answer for this question. – masu Dec 11 '13 at 22:30