While perusing ShreevatsaR's answer to this question, it occurred to me that my own verbal usage is out of step with what I see in current American literature. When speaking in the past tense, I prefer to use the following forms:

• dreamt (past tense of to dream)
• leapt (past tense of to leap)
• swept (past tense of to sweep)
• lit (past tense of to light)

However, when reading recently written novels, I see the more regular conjugation of the past tenses, which instead yields dreamed, leaped, sweeped, and lighted. Is it a difference of dialect (US - New England), register (university education), or (possibly) my age (early forties)? I am especially irritated by "lighted" because it takes so much more effort to say than "lit".

CLARIFICATION: Given Jon Hanna's answer below, I would just like to clarify the question a bit more. What I was originally after was why these separate verb forms exist in the same past tense. In other words, variations such as "I dreamt" vs. "I dreamed", not the variation between different forms in different pasts. I am not a linguist, so I hope that clears things up a bit.