MATLAB used to work on old consoles that had no windowing system. If you called PLOT, then it would switch to graphics mode and draw the plot. You then had to hit ESC or something to get the command line back. If you called plot again, it would start over. There was no handle graphics at the time. Translating this to a window system, it now looks like the following:
% >> do some hard math stuff plot(mydata) % >> think then do more math stuff. plot(mydata)
In this case, the second plot replaces the first, instead of adding to it. If you want two lines in the figure that is where HOLD ON comes in. That is why the axes properties are replaced by default. The question to ask is if the axes had been configured because someone wrote a script that adds titles for instance, should those features stay on the axes when the data is replaced? The answer is no, this is a new fresh plot unless the user specified that it should not be.