No, the screen is quite a bit smaller than A4. A4 = 210 X 297 mm, 10.1 = 137 X 218 mm. (IPad 2 = 147 X 198 mm.) But you can usually display the page without margins. Then the actual text will be larger.
Measure a page in a textbook, without the margins, that is what you will have to display on the screen.
On pages with a lot of small text I sometimes rotate the screen 90 degrees and zoom in to view half a page at a time. Typically scientific magazines. But it is also possible to pinch and zoom where needed with the normal orientation.
If you have the text as a EPUB, then you can of course resize pages freely. You can "reflow" text PDF:s as well, but not always with good results, especially if the layout is complex with illustrations and columns.
It is easier to read on paper, but on the other hand you can almost carry a whole library in the tablet.