The speech to the Dothraki is not something random. They have significance.
This takes us back to S01 E07 "You Win or You Die". Khal Drogo knows that Ser Jorah was ordered by Robert Baratheon to poison Daenerys. But Jorah saves her. Khal Drogo understands and pardons him for saving his Khaleesi and his son. At that point he vows in front of the Dothraki riders.
Khal Drogo : And to my son, the Stallion who mount the world, I will also pledge a gift.
I will give him the iron chair.. that his mother's father sat upon. I will give him the seven kingdoms.
I Drogo will do this. And ride wooden horses across the black salt water....
I will kill the men in iron suits... and tear their stone houses.
I will rape* their women .. take their children as slaves... and break their broken gods to Vaes Dothrak.
This, I vow...I, Drogo son of Bharbo.
These lines are again repeated by Daenerys with Khals at the Temple of the Dosh Khaleen.
So, ascending the iron throne is not only Daenerys's dream due to her claim to the throne. Her ambition got strong due to the vows made by his husband in front of Mother of Mountains.
She planned it to fulfil her husband's vow. Again the same vows are repeated in S0606 "Blood of My Blood". She acquires new khalassar and leads them with her.
I chose you all. I will ask more of you than any Khal has ever asked of his Khalassar!
Will you ride the wooden horses across the black salt sea?
Will you kill my enemies in their iron suits and tear their stone houses?
Will you give me seven kingdoms, the gift Khal Drogo promised me before the Mother of Mountains?
Finally, in the King's Landing, Daenerys speaks:
Blood of my Blood,
You kept all promises to me.
You killed my enemies in their iron suits.
You tore down their stone houses
You gave me seven kingdoms!
So, the speech to Dothraki was not some random words spoken by Daenerys. She was thinking of killing her enemies and destroying them completely if they come in her way to Iron Throne all the way.
* Even though this is not the motive of Daenerys, Dothraki being Dothraki went ahead and misbehaved with the women in the Kings Landing.