What "the tests count for too much" really means

All my student evaluations for Spring '13 are in, and in multiple classes I heard variations of this:

"The tests count for too much of the course grade."

Hmmm.  For large (>50) introductory classes with labs, I typically use the following breakdown:
  Exam 1: 20%
  Exam 2: 20%
  Final: 20%
  Warmup Questions: 15%
  Lab Exercises: 25%

A scan of my department's syllabi from this past semester for large-lecture, introductory courses with labs (not discussion-based courses) found exams worth anywhere from 30 to 70%(!!!) of the course grade.  Skimming some online syllabi from other physical science courses gave similar results--typically around 50 or 60 percent.  One sophomore-level course that shall remain nameless was 80% exam and 20% lab...wow.

In thinking about this, I've come to the conclusion that "tests count for too much" is actually not what my students were trying to tell me.  The true sentiment is probably closer one of these:

1. The tests are too hard.

In some of the other open-ended feedback, students flatly stated they thought my tests were hard.  I don't apologize for that:  they are.  I rarely test the ability to recite simple facts, definitions, and formulas.  I want to see your problem solving skills--what can you do with those definitions?  Of course, this presumes you have the basics in your arsenal in the first place.  If you don't, on my exams, well, you're !(@$ed.  I know people don't like that--I know it's painful--I know it's different--and I also know that problem-solving is a more important academic and life skill than simple memory recall.  That's why my tests are written the way they are.

And/Or,
2.  There's no homework!

This sentiment, a lack of homework, is a good point.  And let's be honest about some of the reasons why homework is a rarity in large lecture courses.  In a class of 60+, homework is difficult to manage, time-consuming to grade, and nearly impossible to return, given that class attendance averages about 75% except the day before an exam.  Yeah, I said it--it's time-consuming.  Professors have lives too, y'all.

An alternative is to farm out the grading to the teaching assistants/associate instructors/graduate students, but that goes against my teaching philosophy.  If I'm responsible for writing and assigning the work, I should be the one to assess it.  I'm the one who truly "knows what I'm looking for."

However, warm-up questions were my alternative.  (If you don't know what these are, read up on Just-in-Time-Teaching.  That's the basic premise.)  They require daily reading assignments, daily submission of answers, are occasionally checked for content, and the answers are discussed in class.  In short:  read the textbook, answer questions before class, get 15% of the grade without even showing up.  That's a pretty good deal, right?  But it doesn't feel like a "real" homework assignment...but, "real" homework wouldn't really be suitable since exams in large courses will be almost entirely multiple choice.  There is no way to keep the assessments consistent in format.

So I'm at a loss about homework.  I like the warmup questions, since they link textbook reading to in-class discussions.  They "test" your basic understanding of the reading, which is the first step toward thinking critically and solving problems...the true goals of (my) exams.

Any thoughts from the gallery?