I think political polls have actually become much less accurate over the last several decades. At one time, when most families had a single publicly-listed land-line telephone, picking a random list of names with only a few controls would produce a representative sampling. Furthermore, there were only a few major polling organizations, so if Gallup called your house, most regarded it as a bit of an opportunity to take part in the civic process and were willing to take the time to provide honest answers.
Today, there are many ways to avoid telephone calls. Furthermore, most people are annoyed because polling in close elections is so frequent, and distrustful because a very large percentage of polls are actually campaign advertisements. The result is that people who have busy lives and the means and sophistication to use wireless or caller IDs probably never speak with pollsters. Random sampling is simply impossible, and the only way for pollsters to generate any meaningful numbers is to carefully normalize the weighting of each demographic group and subgroup according to a pre-definied model. The problem is that those models are fixed, and if there are any unusual factors present (e.g., a property tax issue on the ballot will cause homeowners to turn out, religious voters are strongly motivated by a particular candidate, there's no race in the democratic primary so indepdents will vote in the republican primary), the pollsters can only guess at how that will effect the final numbers.
There are many ways to avoid phone calls ... and my children know them all!
I think this due somewhat to the number of polls now being done. Decades ago, the polls were not reported as news. Now every news agency hires a couple of pollsters to get a feel for public sentiment on wide array of issues. More pollsters dilute the overall quality.
I think that the good polling groups have a handle on the concerns that you raised and have adopted their methodologies for the modern realities. What they have the most problem with is late-deciding voters. In this campaign season, where so many Republicans are unenthusiastic about the candidates, a lot of voters might not make up their minds until they pull the curtain closed.
Other than the NH Democrat primary, the polls have been pretty accurate overall. Of course, when the polls are wrong, it is a big news story. I think this tends to skew our perceptions about the polls' accuracy since we don't hear about the successes.