You have the option of picking up Eldritch Blast (it will count as your single Warlock at-will), but you appear to have an incomplete understanding of the reason why.
Do all warlocks just automatically get Eldritch Blast?
The PHB1 does say this:
Warlock Class Features
You have the following class features:
All warlocks know the eldritch blast at-will power. (and then some more information about it)
When the authors wrote this, Hybrid Warlocks did not exist. They would not exist for another two years. The only kinds of Warlocks that did exist was the kind in this book. What they meant when saying this was that all Warlocks from that book, regardless of the pact they chose, received Eldritch Blast for a power.
Bear in mind the thing saying this is a class feature that Warlocks receive. They receive this class feature because the Class Traits box on page 129 says so. This does not apply to Hybrid Warlocks, because they are not given the Eldritch Blast class feature in their Class Traits box. This is a good thing, because you can still get Eldritch Blast, but it's not required like it would be if you were given the Eldritch Blast class feature.
Can Hybrid Warlocks get Eldritch Blast?
Yes. Or any one of the other at-wills.
First: read page 135, the first page instructing you on how to create a Hybrid character. Two thirds of the way down the right column, it says you choose one at-will from each of your Hybrid classes. Your Warlock at-will choice can be Eldritch Blast.
Second, take note that being a Hybrid Warlock gives you the Eldritch Pact class feature. Normally, one of a Warlock's At-Wills is chosen by their pact. (The other is always Eldritch Blast.) This would mean that you have to take that particular at-will that your pact gives you, except right at the bottom of page 153, after the Class Traits box for the Hybrid Warlock telling you which features you receive, it tells you specifically that your pact doesn't do this.
So you can pick Eldritch Blast for your pact's at-will, or you can choose any of the pact's at-wills. (See the text right under the "Warlock Powers" heading on page 131 if this surprises you: Warlocks can always pick powers intended for other pacts; they just often aren't as powerful as they would be in the hands of the Warlock with the right pact.)