Yes, voters expect presidential hopefuls to express themselves persuasively and forcefully. A candidate who cannot deliver a well-written speech will not connect with voters or make an impression on the national arena. It is a generally accepted practice for candidates to use speechwriters, but even if a candidate has not written the speech themselves, they must present it eloquently to make an impression on their audience.
There is a clear expectation that presidential hopefuls take the time and present well written speeches.
The public does not want to waste their time listening to hollow and uninspiring speeches from the various presidential hopefuls. True and respectful candidates will take the time to deliver well written and inspiring speeches for the public if they really aspire to the presidency.
Everyone knows there are speech writers that contribute to the speeches of the candidates. Everyone has special talents. For candidates it's usually their unique views on where to take the country. They may not be as eloquent as a professional writer, so they utilize their talent to help spruce up their message in the most poignant way possible. This helps them communicate clearly to the public.
Presidential hopefuls should show some aptitude for presenting themselves as presidential. That means that they make some effort at being articulate and that their speeches are understandable. If they speak in rhymes or are simply incoherent, why would voters want them holding the highest elected office in the Land? The President represents the people and the country, at home and abroad. They must be able to communicate clearly.