That statement is only true in the limiting case where you expect everyone to want their money back at any given moment. Modern banks take a calculated risk and assume that there won't be bank runs or anything of that nature. Therefore, the ratio of deposits to loans doesn't, in principle, matter as long as you're not experiencing a run.
Now, in a free market (ie NOT UNITED STATES) banking system, the risk of bank runs may require rational reserve ratios to be much more down to Earth, maybe 3-1 or 4-1, rather than the current 10+. But with the moral hazard of bailouts and hidden bailouts (through a 0% Fed funds rate), banks don't need to really worry about runs, which allows them to go up to higher ratios. Again, you're confusing statist reality with free market reality.