Is it normal for BibTeX to replace similar author names with "------"?

The behavior mentioned is the default using IEEEtran.bst style. To change it, you can define a IEEEtranBSTCTL entry in your bib database and change the default value for CTLdash_repeated_names. So, in this case, your entry should look like this:

@IEEEtranBSTCTL{IEEEexample:BSTcontrol,
  CTLdash_repeated_names = "no"
}

Then in the body of your .tex file you have to activate the change by using

\bstctlcite{IEEEexample:BSTcontrol}

Example (thanks to Marco):

\RequirePackage{filecontents}
\begin{filecontents}{\jobname.bib}
@IEEEtranBSTCTL{IEEEexample:BSTcontrol,
CTLdash_repeated_names= "no",
}

@article{Seshadrinathan2010A-Subjective-St,
    Author = {K. Seshadrinathan and R. Soundararajan and A. C. Bovik and L. K. Cormack},
    title={foo},
    year={2011},
    journal={bla}
}

@article{Seshadrinathan2009Study-of-Subjec,
    Author = {K. Seshadrinathan and R. Soundararajan and A. C. Bovik and L. K. Cormack},
    title={bar},
    year={2010},
    journal={bla}
}
\end{filecontents}

\documentclass{IEEEtran}
%\usepackage{IEEEtrantools}% only needed if a class different from IEEEtran is used.


\begin{document}
\bstctlcite{IEEEexample:BSTcontrol}
\cite{Seshadrinathan2010A-Subjective-St}

\cite{Seshadrinathan2009Study-of-Subjec}


\bibliographystyle{IEEEtran}
\bibliography{\jobname}
\end{document}

To remove the dash, copy the file IEEEtran.bst, located in /bibtex/bst/IEEEtran of your TeX distribution, to your working directory and rename it to myIEEEtran.bst. In the renamed copy, replace

FUNCTION {default.is.dash.repeated.names} { #1 }

with

FUNCTION {default.is.dash.repeated.names} { #0 }

and compile your .tex document using \bibliographystyle{myieeetran}.

EDIT: To the person who downvoted: The original (commented) code in IEEEtran.bst reads

% #0 turns off the "dashification" of repeated (i.e., identical to those
% of the previous entry) names. IEEE normally does this.
% #1 enables
FUNCTION {default.is.dash.repeated.names} { #1 }

so I think the style designer(s) viewed changing #1 to #0 as a valid method of customization.

It depends on the bibliography style. This behavior is normal for style IEEEtrans.

Some bibliography styles are illustrated on the page BibTeX Style Examples.

At this point I recommend the package biblatex where you can set this behavior via the dashed option.

The package itself doesn't provide an IEEEtran style but there is a contrib: biblatex-ieee.