Tense and Lax Vowels

In my English Language class today I learned the different characteristics of the vowels in English. One thing that I thought was really interesting is the Utah or Western States dialect (Sorry, I don't know all the correct terminology yet. Maybe later in the semester). Anyway, many Utahns and other Westerners make many of their vowels lax where others make them tense.
The classic example of this that most people have heard of is creek being pronounced "crick." However, I have not heard this one very much. Ones that I find much more common (and which I do myself) are leg and egg pronounced with the e vowel sound in "end" instead of with the a vowel sound of "age." Another case of making a vowel lax (this one I do not do, but many of my friends do) is making the word "sale" sound the same or very similar to "cell." Other examples that I noticed are "feel" being pronounced as "fill" and "steal" pronounced as "still."
The interesting thing is that the vowels that are switched to lax from tense (or vice versa) are similar in every other aspect (e.g. high, front, unrounded). Thus the switch is partially logical.