Robert is correct. Even in the Standard Interface, you can get the numerical "staircase" effect in plots if you try hard enough. Avoiding this usually involves some reformulation of the problem. For example, you can increase Digits and plot -10*x^5 instead of 1-10*x^5 (using Robert's example), and then use custom labels for the axes tickmarks. I acknowledge that this is not ideal, as it involves some work for the user, but it is usually possible to get a reasonable plot with some effort. At the moment, Maple does not have an automatic way of dealing with such problems.
However, I would urge users who are plotting with the Classic Interface to give the Standard Interface a try. I understand that some users really do need to stick with the Classic Interface for various reasons, but the performance of plots in the Standard Interface has been improving steadily since Maple 9. In Maple 11, my colleagues in the GUI Group made substantial improvements to the performance of 2-D plots, and we are working on more improvements to plotting for future releases.
I myself find it relatively easy to execute a large number of plots in Maple 12. There are also so many really useful plotting features in the Standard Interface: gridlines, transparency, typesetting, true array plots, polar axes, etc. If you're still using Classic, I do hope you'll at least try executing a few plots in Standard. You may be pleasantly surprised.