Because I'm Adwords Certified and manage campaigns for my clients. I frequently aim for mid-page placements because they produce a better ROI - the first slot is great for branding, but if your goal is direct response, sometimes not the best place for it.
First of all, "suggested CPC" is just an estimate. In real life, CPC gets modified by your quality score (on the keyword level) and by what the competing advertisers are doing. And whether your ad shows 100% of the time, 75% of the time, 50% of the time is more related to your daily budget than your CPC.
If you want your ad to be shown 100% of the time in let's say 3rd position for a particular keyword, all you need to do is bid so that your (bid * quality score) for that keyword edges out that of the ad in 4th position and set your daily budget high enough to to cover all the potential clicks.
Likewise, if you're in top position and DON'T have a high enough daily budget, your ad WON'T receive the maximum possible impressions. It will either show 100% and stop when your budget runs out, or be throttled back and shown once every x number of times throughout the day (depending on the option you choose.)
(These examples are for the Search network. Display is a little different because it doesn't look at individual keywords and has options like managed placements and CPM bids, but its similar in how placements are determined.)