Two minipages with 0.5\textwidth each get placed one below another

This happens in the beamer class only. Does anyone know the reason behind this? I fix it by just setting both widths to 0.49\textwidth and this works but I'm still curious why this happens and if I maybe do something wrong.

MWE here:

% !TEX TS-program = pdflatex
% !TEX encoding = UTF-8 Unicode

\documentclass{beamer}
\usetheme{Warsaw}

\begin{document}
\begin{frame}

\begin{minipage}{0.50\textwidth}
asdfasdf
\end{minipage}
\begin{minipage}{0.50\textwidth}
asdfasdf
\end{minipage}

\end{frame}
\end{document}

-
I wrote that already :) But I'm more interested in why this happens and if there is a mistake on my end (misusing the minipage environment e.g.). Also I copy pasted a sligthly altered version of the MWE at first where one width was .5 and the other .49. I'm wondering why .5+0.5 doesn't give me two minipages next to eachother. – Philipp May 2 '12 at 14:31
Ah, sorry for not understanding this point right away. As far as I can tell, you're not making a mistake. – Mico May 2 '12 at 14:33
Beamer provides a columns environment that allows to place things next to each other. It might be a cleaner solution for you (see beamer documentation for details). – yo' May 2 '12 at 14:51
Didn't know about columns but they indeed are a better solution. – Philipp May 3 '12 at 7:26

There is a space between the two minipages so the total of the line is more than \textwidth. Add a % directly after the first \end{minipage}.
nice, thanks! What does the % do? I assume removing spaces but maybe you can give me an accurate answer? TeXshop also includes a % when inserting a table via menu. – Philipp May 2 '12 at 14:35
% is the standard TeX comment character. It gobbles up anything until the end of the line (including the line end which is normally turned into a space). If that is not known to you I suggest you read some intro document on LaTeX as then you are probably missing a lot useful information. Try lshort.pdf for example or any of its translation into some language. – Frank Mittelbach May 2 '12 at 14:39
@Philipp: Have a look at Why the end-of-line % in macro definitions? – Martin Scharrer May 2 '12 at 15:20