On the front of attendance, some of us just have terrible immune systems. I've been taking very good care of myself and have made modifications to my lifestyle and diet in an attempt to increase my health and overall quality of life. However, I do miss about 10 days a year due to illness, 8 so far in this the first year of working from home. When I get sick, I NEVER get stomach problems, it's almost exclusively extreme exhaustion and general 'feverishness'.
When I'm working, I'm very diligent, focused, and hardworking. Enough to make me only the second person my boss has allowed to work from home - The first guy had medical concerns and ended up taking advantage of the situation.
You can be hardworking and still miss days at work. When I miss days, I'm simply not capable of functioning enough to do my job/staying awake. I work in (network) tech support, if you're completely exhausted, it shows. And since I'm primarily involved in more proactive measures that frequently land me in high-priority, potentially explosive situations, being exhausted is not a good thing. Not that I don't do it another dozen plus times a month, I'm just saying that when it's bad enough that you're constantly fighting to stay awake despite energy shots and other measures, it's time to call it quits and be healthy for your next day.