How the text is appended very neatly to the top and bottom of the table?
Probably by placing the table's contents inside a minipage environment of width \textwidth.
The table is the exact same width of the text on the page
Probably with the use of a tabular* environment, with its first argument set to \textwidth.
The width of the columns (which space between columns) seems to have automatically widened to fill up the page width.
The second argument of the tabular* argument was probably set up as follows:
@{}l@{\extracolsep{\fill}}...@{}
% the @{} items suppress whitespace before first and after the last column
% the @{\extracolsep{\fill}} item inserts "\fill" between columns
Putting both elements together, you'd issue the command
\begin{tabular*}{\textwidth}{@{}l@{\extracolsep{\fill}}...@{}`
to start the tabular* environment. Note that the . column type used here would need to be defined by loading the dcolumn package and issuing the command
\newcolumntype{.}{D{.}{.}{-1}}
in the preamble. The -1 instructs dcolumn to try to come up with the best layout ont its own. To fine-tune the layout it's usually a good idea to specify the number of decimal digits (i.e., the ones to the right of the decimal point) explicitly by defining, say, a new column type named d:
\newcolumntype{d}[1]{D{.}{.}{#1}}
The argument indicates the number of digits after the decimal point for which space needs to be reserved.
Finally, to emulate the appearance of the table's caption -- with a newline between the table number and the caption text -- you could load the caption package and issue the command
\captionsetup{labelsep=newline,singlelinecheck=false}
in your document's preamble.
Addendum: Putting all of this together leads to the following MWE, which generates the table you're interested in. First, some notes:
It's not necessary to specify something like \centering for this table because the table takes up the full width of the text block.
Material in "decimal" columns (i.e., those generated by a dcolumn-based specifier) is automatically typeset in TeX's math mode. This is relevant for the \ast macro which typesets a raised asterisk.
I've assigned 4 as the argument of the three d ("decimal-aligned") columns because the asterisks take up one extra space. (Thus, if you had three digits and two asterisks, you'd assign 5 to the number of digits to be set aside by dcolumn, etc.)
I've also used the \toprule, \midrule, and \bottomrule commands provided by the booktabs package instead of the \hline command; the \...rule commands provide for much better vertical spacing that \hline does.
Here, then, is the MWE.

\documentclass[a4paper,11pt]{article}
\usepackage{booktabs,dcolumn,caption}
\captionsetup{labelsep=newline,
singlelinecheck=false,
skip=0.333\baselineskip}
\newcolumntype{d}[1]{D{.}{.}{#1}} % "decimal" column type
\renewcommand{\ast}{{}^{\textstyle *}} % for raised "asterisks"
\begin{document}
\begin{table}[h]
\setlength\tabcolsep{0pt} % let LaTeX figure out amount of inter-column whitespace
\caption{Number of turns and distance between top and bottom.}
\label{turns}
\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}} l *{3}{d{2.4}} }
\toprule
& \multicolumn{3}{c}{AFC Window 1} \\
& \multicolumn{1}{c}{gmt} & \multicolumn{1}{c}{jfk} & \multicolumn{1}{c}{fbi}\\
\midrule
Constant & 0.025\ast & -0.002 & 1.155\ast \\
& (1.22) & (2.22) & (0.56)\\
Constant & 0.025\ast & -0.002 & 1.155\ast \\
& (1.22) & (2.22) & (0.56)\\
Log(assets)\textsuperscript{a}
& 0.025\ast & -0.002 & 1.155\ast \\
& (1.22) & (2.22) & (0.56)\\
\bottomrule
\end{tabular*}
\end{table}
\end{document}
\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}}lccc@{}}And I would remove all the raisebox and[-2ex]negative spacing. – David Carlisle Jul 13 '12 at 16:16booktabspackage. For the number columns, look at theScolumn specifier ofsiunitx(which was probably used). – egreg Jul 13 '12 at 16:28ctableto me – bobobobo Jul 13 '12 at 20:59