Can I replace one of the subplots (in a 2-by-2 matrix) with a table?

You can, but we don't know how wide your paper is?/how much margins you have?/or the documentclass used. However, here are some suggestions:

1. Use a smaller (but still readable) fontsize, footnotesize.
2. Use sanserif shape as it is more readable at smaller fontsize, sffamily.
3. Shrink the inter-column space, setlength{tabcolsep}{2pt}.
4. Add two @{}s around the tabular column specifier to trim any outer space.
5. Last and most important, consider using sidewaysfigure to gain more space.

documentclass[12pt,a4paper]{article}
usepackage[demo]{graphicx}
usepackage[]{subfig}
usepackage{rotating,booktabs}
begin{document}

begin{sidewaysfigure}[hbt!]
    centering
    subfloat[label{Airline:a}]{includegraphics[width=0.46textwidth]{a.eps}} quad
    subfloat[label{Airline:b}]{includegraphics[width=0.46textwidth]{b.eps}} 
    subfloat[label{Airline:c}]{includegraphics[width=0.46textwidth]{c.eps}} quad
    subfloat[label{Airline:d}]{setlength{tabcolsep}{2pt}footnotesizesffamily
    begin{tabular}[b]{@{}lrrrrrrrrrr@{}}
    toprule
    {} &     0 &     1 &     2 &     3 &     4 &     5 &     6 &     7 &     8 &     9 
    midrule
    0  &  0.00 & 14.45 &  9.33 &  9.14 & 10.77 &  7.52 &  8.15 & 11.86 &  9.91 & 11.49 
    1  & 14.45 &  0.00 & 10.13 & 11.73 & 10.17 & 11.12 & 10.61 & 10.74 & 10.09 &  9.93 
    2  &  9.33 & 10.13 &  0.00 &  8.18 &  7.93 &  7.91 &  7.33 &  8.87 &  7.08 &  8.89 
    3  &  9.14 & 11.73 &  8.18 &  0.00 &  9.09 &  6.12 &  9.30 &  8.92 &  7.02 &  8.35 
    4  & 10.77 & 10.17 &  7.93 &  9.09 &  0.00 &  8.00 &  8.78 &  7.58 &  7.38 &  6.01 
    5  &  7.52 & 11.12 &  7.91 &  6.12 &  8.00 &  0.00 &  6.70 &  9.21 &  6.97 &  8.26 
    6  &  8.15 & 10.61 &  7.33 &  9.30 &  8.78 &  6.70 &  0.00 & 10.89 &  8.59 & 10.44 
    7  & 11.86 & 10.74 &  8.87 &  8.92 &  7.58 &  9.21 & 10.89 &  0.00 &  8.47 &  5.43 
    8  &  9.91 & 10.09 &  7.08 &  7.02 &  7.38 &  6.97 &  8.59 &  8.47 &  0.00 &  6.40 
    9  & 11.49 &  9.93 &  8.89 &  8.35 &  6.01 &  8.26 & 10.44 &  5.43 &  6.40 &  0.00 
    bottomrule
    end{tabular}    
    } 
    caption{Descriptive Statistics}
    label{Airline}
end{sidewaysfigure}

end{document}